fix: i18n for dashboard widgets + shortcuts — no more hardcoded French

Replaced all hardcoded French text in dashboard.js with t() calls:
- 'Chargement...' → t('common.loading')
- 'Erreur:' → t('dashboard.error_prefix')
- Size units ('o','Ko','Mo','Go') → t('dashboard.size_*')
- 'fichier(s)' → t('dashboard.count_files*')
- '0 fichiers' → t('dashboard.zero_files')
- 'Conflits de synchronisation' → t('dashboard.conflicts_title')
- 'Garder l\'original'/'Garder le conflit' → t('dashboard.keep_*')
- 'Ajouter/Retirer des bookmarks' → t('dashboard.bookmark_*')
- 'à l\'instant'/'il y a X min/h/j' → t('dashboard.*_ago', {n})
- 'Afficher'/'Masquer' → t('dashboard.show/hide')
- 'Erreur de chargement' → t('dashboard.load_error')

Added 11 shortcut i18n keys + 22 dashboard i18n keys to en.json/fr.json.

Verified: '4 files' count, English shortcuts, English empty states.

frontend/locales/en.json

@@ -447,12 +447,29 @@
   "conflict.resolve_conflict": "Keep conflict version",
   "conflict.resolve_local": "Keep local version",
   "conflict.resolved": "Conflict resolved",
+  "dashboard.all_vaults": "All vaults",
+  "dashboard.bookmark_add": "Add to bookmarks",
+  "dashboard.bookmark_remove": "Remove from bookmarks",
   "dashboard.bookmarks": "Bookmarks",
+  "dashboard.conflict_date": "Conflict of ",
   "dashboard.conflict_resolved": "Conflict resolved",
   "dashboard.conflicts": "Conflicts",
+  "dashboard.conflicts_title": "Sync conflicts",
   "dashboard.copy_btn": "Copy",
+  "dashboard.count_files": "file",
+  "dashboard.count_files_plural": "files",
   "dashboard.ctrl_hover_tip": "Hover over a document with Ctrl for a quick preview. Click Forge in the toolbar for the advanced editor.",
+  "dashboard.day_ago": "{n} d ago",
+  "dashboard.error_prefix": "Error: ",
   "dashboard.expires": "Expires {date}",
+  "dashboard.hide": "Hide",
+  "dashboard.hour_ago": "{n} h ago",
+  "dashboard.just_now": "just now",
+  "dashboard.keep_conflict": "Keep conflict",
+  "dashboard.keep_original": "Keep original",
+  "dashboard.load_error": "Loading error",
+  "dashboard.loading": "Loading...",
+  "dashboard.min_ago": "{n} min ago",
   "dashboard.no_bookmarks": "No bookmarks",
   "dashboard.no_conflicts": "No conflicts",
   "dashboard.no_recent": "No recent files",
@@ -465,6 +482,11 @@
   "dashboard.recent_hint": "Open a file to see it appear here",
   "dashboard.shared_hint": "Share a document to see it appear here",
   "dashboard.shares": "Shares",
+  "dashboard.show": "Show",
+  "dashboard.size_bytes": " B",
+  "dashboard.size_gb": " GB",
+  "dashboard.size_kb": " KB",
+  "dashboard.size_mb": " MB",
   "dashboard.stats": "Statistics",
   "dashboard.stats_files": "Files",
   "dashboard.stats_size": "Total size",
@@ -479,6 +501,7 @@
   "dashboard.vaults_count": "Vaults",
   "dashboard.views": "{count} view(s)",
   "dashboard.welcome": "Welcome to ObsiGate",
+  "dashboard.zero_files": "0 files",
   "dragdrop.cross_vault_unsupported": "Cross-vault moves are not supported",
   "dragdrop.move_failed": "Move failed",
   "editor.cancel": "Cancel",
@@ -1213,6 +1236,17 @@
   "share.never": "Never",
   "share.revoke": "Revoke",
   "share.title": "Public share",
+  "shortcut.ai_completion": "AI inline completion (in editor)",
+  "shortcut.close_editor": "Close editor / modal",
+  "shortcut.command_palette": "Command palette",
+  "shortcut.editor_help": "Forge editor help",
+  "shortcut.file_palette": "File palette (quick nav)",
+  "shortcut.focus_search": "Focus search bar",
+  "shortcut.quick_insert": "Quick insert (Forge editor)",
+  "shortcut.quick_search": "Quick search (outside text field)",
+  "shortcut.save_file": "Save open file",
+  "shortcut.search_in_doc": "Search in document",
+  "shortcut.tip_preview": "Hover a document with **Ctrl** for a quick preview. Click **Forge** in the toolbar for the advanced editor.",
   "sidebar.all_vaults": "All vaults",
   "sidebar.case_sensitive": "Case sensitive",
   "sidebar.clear_filter": "Clear",