i18n: complete remaining roadmap tasks

JS files:
- ai.js: add t() import, replace 10 hardcoded French strings
- sync.js: add t() import, replace 20 hardcoded French strings (toasts, status labels, events, AI panel)
- graph.js: add t() import, replace 6 hardcoded French strings (tooltips, badges)

Locales:
- +36 new keys for ai.js, sync.js, graph.js
- 1206 keys in each locale file (perfectly synchronized)
- 0 French characters remaining in en.json

Documentation:
- README.fr.md created (French version)
- ROADMAP.md point #63 updated to 100% complete

frontend/locales/en.json

@@ -672,7 +672,6 @@
   "auto.caac40b9": "Choose a visual theme. Each theme offers",
   "auto.a3319169": "📦 About",
   "auto.6c166d35": "ObsiGate is your web gateway to your Obsidian vaults. Access, browse, and search all your notes from any device via a modern and responsive interface.",
-  "auto.ca0aceee": "Access",
   "auto.209c5490": "The top bar contains the essential elements:",
   "auto.4c908ade": "Click a vault to open it and see its",
   "auto.1abf6661": "The path displayed above the content is",
@@ -1172,5 +1171,41 @@
   "help.pal_open___select": "Open / select",
   "help.pal_close_the_palette": "Close the palette",
   "help.pal_popout_desc": "Open the document in a detached window",
-  "help.pal_move_desc": "Navigate the list"
+  "help.pal_move_desc": "Navigate the list",
+  "ai.error_invalid_key": "Invalid API key",
+  "ai.edit": "Edit",
+  "ai.hint_improve": "Improves text quality",
+  "ai.hint_add_details": "Adds details",
+  "ai.hint_edit_selection": "Modifies the selected text",
+  "ai.hint_translate": "Translates the selected text",
+  "ai.generate": "Generate",
+  "ai.hint_generate": "Generates content from the selection",
+  "ai.toolbox": "🧰 Toolbox",
+  "ai.rewrite_prompt": "Rewrite instruction:",
+  "sync.vault_added": "Vault \"{vault}\" added ({count} files)",
+  "sync.vault_removed": "Vault \"{vault}\" removed",
+  "sync.index_started": "Indexing started ({count} vaults)",
+  "sync.index_complete": "Indexing complete ({count} files)",
+  "sync.disconnected": "Disconnected",
+  "sync.connected": "Synchronized",
+  "sync.updating": "Updating...",
+  "sync.connected_short": "Connected",
+  "sync.no_recent_events": "No recent events",
+  "sync.event_index_updated": "Update",
+  "sync.event_vault_added": "Vault added",
+  "sync.event_vault_removed": "Vault removed",
+  "sync.event_index_start": "Index starting",
+  "sync.event_index_progress": "Vault indexed",
+  "sync.verifying": "Verifying…",
+  "sync.autocomplete_active": "Autocomplete active",
+  "sync.model_not_loaded": "Model not loaded",
+  "sync.not_configured": "Not configured",
+  "sync.autocomplete": "Autocomplete",
+  "sync.update": "Update",
+  "graph.category": "📂 Category",
+  "graph.published": "Published",
+  "graph.ctrl_hover_preview": "Ctrl+hover = full preview",
+  "graph.published_badge": "✅ published",
+  "graph.click_to_open": "click to open",
+  "graph.ctrl_hover_preview_short": "Ctrl+hover = preview"
 }