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/js/sync.js

@@ -1,5 +1,6 @@
 /* ObsiGate — Sync: SSE client + PWA registration + Offline mode */
 import { state } from './state.js';
+import { t } from './i18n.js';
 import { showToast } from './ui.js';
 import { api } from './auth.js';
 import { loadVaults, loadTags, refreshTagsForContext, refreshSidebarTreePreservingState } from './sidebar.js';
@@ -59,7 +60,7 @@ export const IndexUpdateManager = (() => {
       try {
         const data = JSON.parse(e.data);
         _addEvent("vault_added", data);
-        showToast(`Vault "${data.vault}" ajouté (${data.stats.file_count} fichiers)`, "info");
+        showToast(t('sync.vault_added', { vault: data.vault, count: data.stats.file_count }), "info");
         loadVaults();
         loadTags();
       } catch (err) {
@@ -71,7 +72,7 @@ export const IndexUpdateManager = (() => {
       try {
         const data = JSON.parse(e.data);
         _addEvent("vault_removed", data);
-        showToast(`Vault "${data.vault}" supprimé`, "info");
+        showToast(t('sync.vault_removed', { vault: data.vault }), "info");
         loadVaults();
         loadTags();
       } catch (err) {
@@ -85,7 +86,7 @@ export const IndexUpdateManager = (() => {
         _addEvent("index_start", data);
         connectionState = "syncing";
         _updateBadge();
-        showToast(`Indexation démarrée (${data.total_vaults} vaults)`, "info");
+        showToast(t('sync.index_started', { count: data.total_vaults }), "info");
       } catch (err) {
         console.error("SSE parse error:", err);
       }
@@ -110,7 +111,7 @@ export const IndexUpdateManager = (() => {
         _addEvent("index_complete", data);
         connectionState = "connected";
         _updateBadge();
-        showToast(`Indexation terminée (${data.total_files} fichiers)`, "success");
+        showToast(t('sync.index_complete', { count: data.total_files }), "success");
         loadVaults();
         loadTags();
       } catch (err) {
@@ -204,10 +205,10 @@ export const IndexUpdateManager = (() => {
     if (!badge) return;
     badge.className = "sync-badge sync-badge--" + connectionState;
     const labels = {
-      disconnected: "Déconnecté",
+      disconnected: t('sync.disconnected'),
       connecting: "Connexion...",
-      connected: "Synchronisé",
-      syncing: "Mise à jour...",
+      connected: t('sync.connected'),
+      syncing: t('sync.updating'),
     };
     badge.title = labels[connectionState] || connectionState;
   }
@@ -289,9 +290,9 @@ function _renderSyncPanel(panel) {
   const events = IndexUpdateManager.getRecentEvents();
 
   const stateLabels = {
-    disconnected: "Déconnecté",
+    disconnected: t('sync.disconnected'),
     connecting: "Connexion...",
-    connected: "Connecté",
+    connected: t('sync.connected_short'),
     syncing: "Synchronisation...",
   };
 
@@ -301,18 +302,18 @@ function _renderSyncPanel(panel) {
   </div>`;
 
   if (events.length === 0) {
-    html += `<div class="sync-panel__empty">Aucun événement récent</div>`;
+    html += `<div class="sync-panel__empty">${t('sync.no_recent_events')}</div>`;
   } else {
     html += `<div class="sync-panel__events">`;
     events.slice(0, 10).forEach((ev) => {
       const time = new Date(ev.timestamp).toLocaleTimeString();
       const typeLabels = {
-        index_updated: "Mise à jour",
+        index_updated: t('sync.event_index_updated'),
         index_reloaded: "Rechargement",
-        vault_added: "Vault ajouté",
-        vault_removed: "Vault supprimé",
-        index_start: "Démarrage index.",
-        index_progress: "Vault indexé",
+        vault_added: t('sync.event_vault_added'),
+        vault_removed: t('sync.event_vault_removed'),
+        index_start: t('sync.event_index_start'),
+        index_progress: t('sync.event_index_progress'),
         index_complete: "Indexation tech.",
       };
       const label = typeLabels[ev.type] || ev.type;
@@ -378,7 +379,7 @@ function _renderAIStatusSection(panel) {
     extClass = 'sync-panel__ai--inactive';
   } else {
     extIcon = 'help-circle';
-    extText = 'Vérification…';
+    extText = t('sync.verifying');
     extClass = 'sync-panel__ai--unknown';
   }
 
@@ -386,11 +387,11 @@ function _renderAIStatusSection(panel) {
   let acIcon, acText, acClass;
   if (_aiAutocomplete && _aiAutocomplete.available) {
     acIcon = 'check-circle';
-    acText = 'Auto-complétion active';
+    acText = t('sync.autocomplete_active');
     acClass = 'sync-panel__ai--active';
   } else if (_aiAutocomplete && _aiAutocomplete.server_ok && !_aiAutocomplete.model_loaded) {
     acIcon = 'alert-triangle';
-    acText = 'Modèle non chargé';
+    acText = t('sync.model_not_loaded');
     acClass = 'sync-panel__ai--inactive';
   } else if (_aiAutocomplete && _aiAutocomplete.error) {
     acIcon = 'x-circle';
@@ -398,11 +399,11 @@ function _renderAIStatusSection(panel) {
     acClass = 'sync-panel__ai--inactive';
   } else if (_aiAutocomplete === null) {
     acIcon = 'help-circle';
-    acText = 'Vérification…';
+    acText = t('sync.verifying');
     acClass = 'sync-panel__ai--unknown';
   } else {
     acIcon = 'x-circle';
-    acText = 'Non configuré';
+    acText = t('sync.not_configured');
     acClass = 'sync-panel__ai--inactive';
   }
 
@@ -416,7 +417,7 @@ function _renderAIStatusSection(panel) {
       '</span>' +
     '</div>' +
     '<div class="sync-panel__ai-row">' +
-      '<span class="sync-panel__ai-label">Auto-complétion</span>' +
+      '<span class="sync-panel__ai-label">' + t('sync.autocomplete') + '</span>' +
       '<span class="sync-panel__ai-state ' + acClass + '" data-lucide-icon="' + acIcon + '">' +
         '<i data-lucide="' + acIcon + '" style="width:14px;height:14px"></i>' +
         acText +