feat: i18n system - French/English internationalization

Core: i18n.js module with t(), setLocale(), initI18n()
- Flat key→string JSON locale files (fr.json + en.json, 165 keys)
- data-i18n / data-i18n-placeholder / data-i18n-attr DOM attributes
- Live locale switch via setLocale() - no page reload
- Language detection: localStorage > navigator.language > 'fr'
- Fallback: missing key → French → raw key

Wired into:
- app.js: await initI18n() early in init()
- config.js: profile save → await setLocale(), toasts + confirm via t()
- auth.js: network error toast via t()
- index.html: data-i18n on login form, profile section, search placeholder

frontend/locales/en.json

@@ -0,0 +1,271 @@
+{
+  "_meta": { "locale": "en", "name": "English" },
+
+  "header.logo": "ObsiGate",
+  "header.search_placeholder": "Search all vaults...",
+  "header.config": "Settings",
+  "header.help": "Help",
+  "header.profile": "Profile",
+  "header.logout": "Sign out",
+  "header.refresh": "Refresh",
+  "header.install_app": "Install app",
+  "header.admin_panel": "Administration",
+
+  "sidebar.filter_placeholder": "Filter files...",
+  "sidebar.tab_vaults": "Vaults",
+  "sidebar.tab_tags": "Tags",
+  "sidebar.tab_recent": "Recent",
+  "sidebar.tab_saved": "Searches",
+  "sidebar.loading": "Loading...",
+  "sidebar.no_results": "No results",
+  "sidebar.vault_context_all": "All vaults",
+
+  "search.operators_help": "Operators: tag:word, vault:name, title:word, path:word, ext:md",
+  "search.results_count": "{count} result(s)",
+  "search.no_results": "No results found",
+  "search.loading": "Searching...",
+  "search.error": "Search error",
+  "search.save_search": "Save search",
+  "search.sort_relevance": "Relevance",
+  "search.sort_date": "Date",
+  "search.sort_title": "Title",
+  "search.facet_tags": "Tags",
+  "search.facet_vaults": "Vaults",
+  "search.filters": "Filters",
+  "search.case_sensitive": "Case sensitive",
+  "search.whole_word": "Whole word",
+  "search.regex": "Regular expression",
+
+  "viewer.source": "Source",
+  "viewer.markdown": "Markdown",
+  "viewer.edit": "Edit",
+  "viewer.raw": "Raw",
+  "viewer.copy": "Copy",
+  "viewer.popout": "Open in popup",
+  "viewer.download": "Download",
+  "viewer.share": "Share",
+  "viewer.backlinks": "Backlinks",
+  "viewer.toc": "Table of contents",
+  "viewer.outline": "Outline",
+  "viewer.loading": "Loading file...",
+  "viewer.error": "Loading error",
+  "viewer.binary_unsupported": "Unsupported binary file",
+  "viewer.binary_download": "Download file",
+  "viewer.pdf_pages": "{count} pages",
+
+  "editor.save": "Save",
+  "editor.cancel": "Cancel",
+  "editor.saved": "Saved ✓",
+  "editor.unsaved": "Unsaved changes",
+  "editor.find": "Find in file...",
+  "editor.replace": "Replace",
+  "editor.find_regex": "Regex",
+  "editor.find_case": "Case sensitive",
+  "editor.find_whole": "Whole word",
+  "editor.no_results": "No results",
+  "editor.close": "Close",
+
+  "ai.toolbar_edit": "Edit",
+  "ai.toolbar_tone": "Tone",
+  "ai.toolbar_translate": "Translate",
+  "ai.toolbar_generate": "Generate",
+  "ai.toolbar_rewrite": "Rewrite",
+  "ai.toolbar_toolbox": "Toolbox",
+  "ai.improve": "Improve",
+  "ai.fix_spelling": "Fix spelling",
+  "ai.shorter": "Shorter",
+  "ai.longer": "Longer",
+  "ai.simplify": "Simplify",
+  "ai.professional": "Professional tone",
+  "ai.casual": "Casual tone",
+  "ai.translate_to": "Translate to {lang}",
+  "ai.explain": "Explain",
+  "ai.summarize": "Summarize",
+  "ai.continue": "Continue",
+  "ai.to_list": "Convert to list",
+  "ai.to_table": "Convert to table",
+  "ai.frontmatter": "Generate frontmatter",
+  "ai.to_canvas": "Convert to Canvas",
+  "ai.custom_rewrite": "Custom rewrite",
+  "ai.no_api_key": "No API key configured",
+  "ai.select_text": "Select text to process",
+  "ai.done": "AI: text processed",
+
+  "dashboard.welcome": "Welcome to ObsiGate",
+  "dashboard.stats": "Statistics",
+  "dashboard.bookmarks": "Bookmarks",
+  "dashboard.conflicts": "Conflicts",
+  "dashboard.recent": "Recent",
+  "dashboard.total_files": "Total files",
+  "dashboard.total_tags": "Unique tags",
+  "dashboard.total_size": "Total size",
+  "dashboard.vaults_count": "Vaults",
+  "dashboard.no_bookmarks": "No bookmarks",
+  "dashboard.no_conflicts": "No conflicts",
+  "dashboard.no_recent": "No recent files",
+
+  "config.title": "Settings",
+  "config.profile": "User profile",
+  "config.profile_desc": "Personal preferences to customize your ObsiGate experience.",
+  "config.lang_label": "Preferred language",
+  "config.lang_hint": "Used by autocomplete and ghost text.",
+  "config.display_name": "Display name",
+  "config.save": "Save",
+  "config.logout": "Sign out",
+  "config.saved": "✓ Saved",
+  "config.about": "About",
+  "config.about_loading": "Loading...",
+  "config.about_error": "Loading error",
+  "config.ai_keys": "AI API keys",
+  "config.ai_keys_desc": "Configure API keys for the AI editor.",
+  "config.hidden_files": "Hidden files",
+  "config.hidden_files_desc": "Manage display of hidden files and folders.",
+  "config.webhooks": "Webhooks",
+  "config.webhooks_desc": "HTTP notifications to external services on file changes.",
+  "config.shares": "Public shares",
+  "config.shares_desc": "Manage public share links for your documents.",
+  "config.backups": "Backups",
+  "config.backups_desc": "Manage automatic file backups.",
+  "config.diagnostics": "Diagnostics",
+  "config.diagnostics_desc": "Technical information about the server state.",
+  "config.reindex": "Reindex",
+  "config.reindex_desc": "Rebuild the search index for all vaults.",
+  "config.client_config": "Client configuration",
+  "config.server_config": "Server configuration",
+
+  "help.title": "ObsiGate Help",
+  "help.shortcuts": "Keyboard shortcuts",
+  "help.search_operators": "Search operators",
+  "help.markdown": "Markdown syntax",
+  "help.about": "About",
+
+  "auth.login_title": "Secure access to your vaults",
+  "auth.username": "Username",
+  "auth.password": "Password",
+  "auth.login_button": "Sign in",
+  "auth.remember_me": "Remember me",
+  "auth.login_error": "Invalid credentials",
+  "auth.network_error": "Network error — check your connection",
+  "auth.logged_out": "Signed out",
+  "auth.session_expired": "Session expired, please sign in again",
+
+  "share.title": "Public share",
+  "share.create": "Create share link",
+  "share.copy_link": "Copy link",
+  "share.revoke": "Revoke",
+  "share.expires": "Expires on",
+  "share.never": "Never",
+  "share.copied": "Link copied!",
+
+  "backup.title": "Backups",
+  "backup.restore": "Restore",
+  "backup.delete": "Delete",
+  "backup.diff": "Compare",
+  "backup.purge": "Purge",
+  "backup.no_backups": "No backups",
+  "backup.preview": "Preview",
+  "backup.version": "Version from {date}",
+
+  "graph.title": "Graph",
+  "graph.fullscreen": "Full screen",
+  "graph.export_png": "Export PNG",
+  "graph.depth": "Depth",
+  "graph.filter_tag": "Filter by tag",
+  "graph.filter_type": "Filter by type",
+  "graph.focus_mode": "Focus mode",
+  "graph.back": "Back",
+  "graph.forward": "Forward",
+  "graph.parent": "Parent",
+  "graph.loading": "Building graph...",
+
+  "mermaid.code": "Code",
+  "mermaid.preview": "Preview",
+  "mermaid.copy_svg": "Copy SVG",
+  "mermaid.download_png": "Download PNG",
+  "mermaid.zoom_in": "Zoom in",
+  "mermaid.zoom_out": "Zoom out",
+
+  "palette.search_files": "Search files...",
+  "palette.search_commands": "Type a command...",
+
+  "offline.status": "Offline",
+  "offline.pending": "{count} pending change(s)",
+  "offline.sync_now": "Sync now",
+  "offline.conflict_title": "Sync conflict",
+  "offline.keep_local": "Keep local version",
+  "offline.keep_server": "Keep server version",
+
+  "conflict.resolve_local": "Keep local version",
+  "conflict.resolve_conflict": "Keep conflict version",
+  "conflict.no_conflicts": "No conflicts detected",
+  "conflict.resolved": "Conflict resolved",
+
+  "common.loading": "Loading...",
+  "common.error": "Error",
+  "common.ok": "OK",
+  "common.cancel": "Cancel",
+  "common.close": "Close",
+  "common.save": "Save",
+  "common.delete": "Delete",
+  "common.confirm": "Confirm",
+  "common.yes": "Yes",
+  "common.no": "No",
+  "common.search": "Search",
+  "common.create": "Create",
+  "common.edit": "Edit",
+  "common.rename": "Rename",
+  "common.move": "Move",
+  "common.copy": "Copy",
+  "common.copied": "Copied!",
+  "common.download": "Download",
+  "common.refresh": "Refresh",
+  "common.back": "Back",
+  "common.next": "Next",
+  "common.previous": "Previous",
+  "common.all": "All",
+  "common.none": "None",
+  "common.actions": "Actions",
+
+  "toast.saved": "Saved",
+  "toast.deleted": "Deleted",
+  "toast.created": "Created",
+  "toast.renamed": "Renamed",
+  "toast.moved": "Moved",
+  "toast.copied": "Copied!",
+  "toast.error_rename": "Cannot rename this item",
+  "toast.error_delete": "Delete error",
+  "toast.error_load": "Loading error",
+  "toast.error_network": "Network error",
+  "toast.reindex_started": "Reindexing...",
+  "toast.reindex_done": "Reindexing complete",
+  "toast.index_reloaded": "Full index reloaded",
+  "toast.installed": "ObsiGate installed successfully!",
+  "toast.not_found_tree": "Item not found in tree",
+  "toast.config_saved": "Configuration saved",
+  "toast.config_client_saved": "Client settings saved",
+  "toast.config_reset": "Configuration reset",
+
+  "confirm.logout": "Are you sure you want to sign out?",
+  "confirm.delete_file": "Permanently delete this file?",
+  "confirm.delete_dir": "Delete this folder and all its contents?",
+
+  "pwa.install_title": "Install ObsiGate",
+  "pwa.install_desc": "Install this app on your device for quick access.",
+  "pwa.install_button": "Install",
+  "pwa.dismiss": "Later",
+
+  "file.new_file": "New file",
+  "file.new_folder": "New folder",
+  "file.rename": "Rename",
+  "file.delete": "Delete",
+  "file.copy_path": "Copy path",
+  "file.properties": "Properties",
+  "file.graph_view": "Graph view",
+
+  "vault.add_dynamic": "Add vault",
+  "vault.remove_dynamic": "Remove vault",
+  "vault.reindex": "Reindex vault",
+
+  "theme.light": "Light",
+  "theme.dark": "Dark"
+}

frontend/locales/fr.json

@@ -0,0 +1,271 @@
+{
+  "_meta": { "locale": "fr", "name": "Français" },
+
+  "header.logo": "ObsiGate",
+  "header.search_placeholder": "Rechercher dans toutes les vaults...",
+  "header.config": "Configuration",
+  "header.help": "Aide",
+  "header.profile": "Profil",
+  "header.logout": "Déconnexion",
+  "header.refresh": "Rafraîchir",
+  "header.install_app": "Installer l'application",
+  "header.admin_panel": "Administration",
+
+  "sidebar.filter_placeholder": "Filtrer fichiers...",
+  "sidebar.tab_vaults": "Vaults",
+  "sidebar.tab_tags": "Tags",
+  "sidebar.tab_recent": "Récents",
+  "sidebar.tab_saved": "Recherches",
+  "sidebar.loading": "Chargement...",
+  "sidebar.no_results": "Aucun résultat",
+  "sidebar.vault_context_all": "Toutes les vaults",
+
+  "search.operators_help": "Opérateurs : tag:mot, vault:nom, title:mot, path:mot, ext:md",
+  "search.results_count": "{count} résultat(s)",
+  "search.no_results": "Aucun résultat trouvé",
+  "search.loading": "Recherche en cours...",
+  "search.error": "Erreur de recherche",
+  "search.save_search": "Sauvegarder la recherche",
+  "search.sort_relevance": "Pertinence",
+  "search.sort_date": "Date",
+  "search.sort_title": "Titre",
+  "search.facet_tags": "Tags",
+  "search.facet_vaults": "Vaults",
+  "search.filters": "Filtres",
+  "search.case_sensitive": "Respecter la casse",
+  "search.whole_word": "Mot entier",
+  "search.regex": "Expression régulière",
+
+  "viewer.source": "Source",
+  "viewer.markdown": "Markdown",
+  "viewer.edit": "Éditer",
+  "viewer.raw": "Brut",
+  "viewer.copy": "Copier",
+  "viewer.popout": "Ouvrir dans une fenêtre",
+  "viewer.download": "Télécharger",
+  "viewer.share": "Partager",
+  "viewer.backlinks": "Backlinks",
+  "viewer.toc": "Table des matières",
+  "viewer.outline": "Plan",
+  "viewer.loading": "Chargement du fichier...",
+  "viewer.error": "Erreur de chargement",
+  "viewer.binary_unsupported": "Fichier binaire non supporté",
+  "viewer.binary_download": "Télécharger le fichier",
+  "viewer.pdf_pages": "{count} pages",
+
+  "editor.save": "Enregistrer",
+  "editor.cancel": "Annuler",
+  "editor.saved": "Sauvegardé ✓",
+  "editor.unsaved": "Modifications non sauvegardées",
+  "editor.find": "Rechercher dans le fichier...",
+  "editor.replace": "Remplacer",
+  "editor.find_regex": "Regex",
+  "editor.find_case": "Respecter la casse",
+  "editor.find_whole": "Mot entier",
+  "editor.no_results": "Aucun résultat",
+  "editor.close": "Fermer",
+
+  "ai.toolbar_edit": "Éditer",
+  "ai.toolbar_tone": "Ton",
+  "ai.toolbar_translate": "Traduire",
+  "ai.toolbar_generate": "Générer",
+  "ai.toolbar_rewrite": "Réécrire",
+  "ai.toolbar_toolbox": "Toolbox",
+  "ai.improve": "Améliorer",
+  "ai.fix_spelling": "Corriger l'orthographe",
+  "ai.shorter": "Raccourcir",
+  "ai.longer": "Allonger",
+  "ai.simplify": "Simplifier",
+  "ai.professional": "Ton professionnel",
+  "ai.casual": "Ton décontracté",
+  "ai.translate_to": "Traduire en {lang}",
+  "ai.explain": "Expliquer",
+  "ai.summarize": "Résumer",
+  "ai.continue": "Continuer",
+  "ai.to_list": "Convertir en liste",
+  "ai.to_table": "Convertir en tableau",
+  "ai.frontmatter": "Générer frontmatter",
+  "ai.to_canvas": "Convertir en Canvas",
+  "ai.custom_rewrite": "Réécriture personnalisée",
+  "ai.no_api_key": "Aucune clé API configurée",
+  "ai.select_text": "Sélectionnez du texte à traiter",
+  "ai.done": "AI: texte traité",
+
+  "dashboard.welcome": "Bienvenue dans ObsiGate",
+  "dashboard.stats": "Statistiques",
+  "dashboard.bookmarks": "Favoris",
+  "dashboard.conflicts": "Conflits",
+  "dashboard.recent": "Récents",
+  "dashboard.total_files": "Fichiers totaux",
+  "dashboard.total_tags": "Tags uniques",
+  "dashboard.total_size": "Taille totale",
+  "dashboard.vaults_count": "Vaults",
+  "dashboard.no_bookmarks": "Aucun favori",
+  "dashboard.no_conflicts": "Aucun conflit",
+  "dashboard.no_recent": "Aucun fichier récent",
+
+  "config.title": "Configuration",
+  "config.profile": "Profil utilisateur",
+  "config.profile_desc": "Préférences personnelles pour personnaliser l'expérience ObsiGate.",
+  "config.lang_label": "Langue préférée",
+  "config.lang_hint": "Utilisée par l'autocomplétion et le ghost text.",
+  "config.display_name": "Nom d'affichage",
+  "config.save": "Enregistrer",
+  "config.logout": "Déconnexion",
+  "config.saved": "✓ Sauvegardé",
+  "config.about": "À propos",
+  "config.about_loading": "Chargement...",
+  "config.about_error": "Erreur de chargement",
+  "config.ai_keys": "Clés API IA",
+  "config.ai_keys_desc": "Configurez les clés API pour l'éditeur IA.",
+  "config.hidden_files": "Fichiers cachés",
+  "config.hidden_files_desc": "Gérez l'affichage des fichiers et dossiers cachés.",
+  "config.webhooks": "Webhooks",
+  "config.webhooks_desc": "Notifications HTTP vers des services externes lors des changements de fichiers.",
+  "config.shares": "Partages publics",
+  "config.shares_desc": "Gérez les liens de partage public de vos documents.",
+  "config.backups": "Sauvegardes",
+  "config.backups_desc": "Gérez les sauvegardes automatiques de vos fichiers.",
+  "config.diagnostics": "Diagnostics",
+  "config.diagnostics_desc": "Informations techniques sur l'état du serveur.",
+  "config.reindex": "Réindexer",
+  "config.reindex_desc": "Reconstruire l'index de recherche pour toutes les vaults.",
+  "config.client_config": "Configuration client",
+  "config.server_config": "Configuration serveur",
+
+  "help.title": "Aide ObsiGate",
+  "help.shortcuts": "Raccourcis clavier",
+  "help.search_operators": "Opérateurs de recherche",
+  "help.markdown": "Syntaxe Markdown",
+  "help.about": "À propos",
+
+  "auth.login_title": "Connexion",
+  "auth.username": "Nom d'utilisateur",
+  "auth.password": "Mot de passe",
+  "auth.login_button": "Se connecter",
+  "auth.remember_me": "Se souvenir de moi",
+  "auth.login_error": "Identifiants invalides",
+  "auth.network_error": "Erreur réseau — vérifiez votre connexion",
+  "auth.logged_out": "Déconnecté",
+  "auth.session_expired": "Session expirée, veuillez vous reconnecter",
+
+  "share.title": "Partage public",
+  "share.create": "Créer un lien de partage",
+  "share.copy_link": "Copier le lien",
+  "share.revoke": "Révoquer",
+  "share.expires": "Expire le",
+  "share.never": "Jamais",
+  "share.copied": "Lien copié !",
+
+  "backup.title": "Sauvegardes",
+  "backup.restore": "Restaurer",
+  "backup.delete": "Supprimer",
+  "backup.diff": "Comparer",
+  "backup.purge": "Purger",
+  "backup.no_backups": "Aucune sauvegarde",
+  "backup.preview": "Aperçu",
+  "backup.version": "Version du {date}",
+
+  "graph.title": "Graphe",
+  "graph.fullscreen": "Plein écran",
+  "graph.export_png": "Exporter PNG",
+  "graph.depth": "Profondeur",
+  "graph.filter_tag": "Filtrer par tag",
+  "graph.filter_type": "Filtrer par type",
+  "graph.focus_mode": "Mode focus",
+  "graph.back": "Retour",
+  "graph.forward": "Avancer",
+  "graph.parent": "Parent",
+  "graph.loading": "Construction du graphe...",
+
+  "mermaid.code": "Code",
+  "mermaid.preview": "Aperçu",
+  "mermaid.copy_svg": "Copier SVG",
+  "mermaid.download_png": "Télécharger PNG",
+  "mermaid.zoom_in": "Zoom avant",
+  "mermaid.zoom_out": "Zoom arrière",
+
+  "palette.search_files": "Rechercher un fichier...",
+  "palette.search_commands": "Tapez une commande...",
+
+  "offline.status": "Hors-ligne",
+  "offline.pending": "{count} modification(s) en attente",
+  "offline.sync_now": "Synchroniser maintenant",
+  "offline.conflict_title": "Conflit de synchronisation",
+  "offline.keep_local": "Garder version locale",
+  "offline.keep_server": "Garder version serveur",
+
+  "conflict.resolve_local": "Garder version locale",
+  "conflict.resolve_conflict": "Garder version conflit",
+  "conflict.no_conflicts": "Aucun conflit détecté",
+  "conflict.resolved": "Conflit résolu",
+
+  "common.loading": "Chargement...",
+  "common.error": "Erreur",
+  "common.ok": "OK",
+  "common.cancel": "Annuler",
+  "common.close": "Fermer",
+  "common.save": "Enregistrer",
+  "common.delete": "Supprimer",
+  "common.confirm": "Confirmer",
+  "common.yes": "Oui",
+  "common.no": "Non",
+  "common.search": "Rechercher",
+  "common.create": "Créer",
+  "common.edit": "Éditer",
+  "common.rename": "Renommer",
+  "common.move": "Déplacer",
+  "common.copy": "Copier",
+  "common.copied": "Copié !",
+  "common.download": "Télécharger",
+  "common.refresh": "Rafraîchir",
+  "common.back": "Retour",
+  "common.next": "Suivant",
+  "common.previous": "Précédent",
+  "common.all": "Tous",
+  "common.none": "Aucun",
+  "common.actions": "Actions",
+
+  "toast.saved": "Sauvegardé",
+  "toast.deleted": "Supprimé",
+  "toast.created": "Créé",
+  "toast.renamed": "Renommé",
+  "toast.moved": "Déplacé",
+  "toast.copied": "Copié !",
+  "toast.error_rename": "Impossible de renommer cet élément",
+  "toast.error_delete": "Erreur de suppression",
+  "toast.error_load": "Erreur de chargement",
+  "toast.error_network": "Erreur réseau",
+  "toast.reindex_started": "Réindexation en cours...",
+  "toast.reindex_done": "Réindexation terminée",
+  "toast.index_reloaded": "Index complet rechargé",
+  "toast.installed": "ObsiGate installé avec succès !",
+  "toast.not_found_tree": "Élément introuvable dans l'arborescence",
+  "toast.config_saved": "Configuration sauvegardée",
+  "toast.config_client_saved": "Paramètres client sauvegardés",
+  "toast.config_reset": "Configuration réinitialisée",
+
+  "confirm.logout": "Voulez-vous vraiment vous déconnecter ?",
+  "confirm.delete_file": "Supprimer définitivement ce fichier ?",
+  "confirm.delete_dir": "Supprimer ce dossier et tout son contenu ?",
+
+  "pwa.install_title": "Installer ObsiGate",
+  "pwa.install_desc": "Installez cette application sur votre appareil pour un accès rapide.",
+  "pwa.install_button": "Installer",
+  "pwa.dismiss": "Plus tard",
+
+  "file.new_file": "Nouveau fichier",
+  "file.new_folder": "Nouveau dossier",
+  "file.rename": "Renommer",
+  "file.delete": "Supprimer",
+  "file.copy_path": "Copier le chemin",
+  "file.properties": "Propriétés",
+  "file.graph_view": "Vue graphe",
+
+  "vault.add_dynamic": "Ajouter une vault",
+  "vault.remove_dynamic": "Retirer la vault",
+  "vault.reindex": "Réindexer la vault",
+
+  "theme.light": "Clair",
+  "theme.dark": "Sombre"
+}