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/graph.js

@@ -1,6 +1,7 @@
 /* ObsiGate — Graph View: interactive file/folder relationship visualization.
    Phase 2: theme colors, tooltips, depth slider, full-vault, search, backlinks. */
 import { api } from './auth.js';
+import { t } from './i18n.js';
 import { safeCreateIcons } from './utils.js';
 import { openFile } from './viewer.js';
 
@@ -624,8 +625,8 @@ export const GraphViewManager = {
       if (fm.auteur) rows.push(`<div><span style="color:var(--text-muted)">✍️ Auteur</span> <span>${fm.auteur}</span></div>`);
       if (fm.date || fm.creation_date) rows.push(`<div><span style="color:var(--text-muted)">📅 Date</span> <span>${fm.date || fm.creation_date}</span></div>`);
       if (fm.statut) rows.push(`<div><span style="color:var(--text-muted)">📌 Statut</span> <span>${fm.statut}</span></div>`);
-      if (fm.catégorie || fm.categorie) rows.push(`<div><span style="color:var(--text-muted)">📂 Catégorie</span> <span>${fm.catégorie || fm.categorie}</span></div>`);
-      if (fm.publish) rows.push('<div><span style="color:var(--text-muted)">✅</span> <span>Publié</span></div>');
+      if (fm.catégorie || fm.categorie) rows.push(`<div><span style="color:var(--text-muted)">${t('graph.category')}</span> <span>${fm.catégorie || fm.categorie}</span></div>`);
+      if (fm.publish) rows.push('<div><span style="color:var(--text-muted)">✅</span> <span>${t('graph.published')}</span></div>');
       if (fm.favoris) rows.push('<div><span style="color:var(--text-muted)">⭐</span> <span>Favoris</span></div>');
       if (rows.length > 0) metaRows = rows.join('');
     }
@@ -649,7 +650,7 @@ export const GraphViewManager = {
       </div>
       ${metaRows ? `<div style="font-size:0.72rem;display:flex;flex-direction:column;gap:2px;padding:6px 0;border-top:1px solid var(--border-color);border-bottom:1px solid var(--border-color);margin-bottom:6px">${metaRows}</div>` : ''}
       ${tags.length > 0 ? `<div style="display:flex;gap:4px;flex-wrap:wrap">${tags.map(t => `<span style="font-size:0.65rem;background:var(--accent-color);color:#fff;padding:1px 6px;border-radius:3px;opacity:0.8">#${t}</span>`).join('')}</div>` : ''}
-      ${node.type === 'file' ? '<div style="font-size:0.6rem;color:var(--text-muted);margin-top:6px;opacity:0.6">Ctrl+survol = aperçu complet</div>' : ''}
+      ${node.type === 'file' ? '<div style="font-size:0.6rem;color:var(--text-muted);margin-top:6px;opacity:0.6">${t('graph.ctrl_hover_preview')}</div>' : ''}
     `;
     this._infoPanel.style.display = 'block';
   },
@@ -671,7 +672,7 @@ export const GraphViewManager = {
       if (fm.auteur) items.push(`✍️ ${fm.auteur}`);
       if (fm.date || fm.creation_date) items.push(`📅 ${fm.date || fm.creation_date}`);
       if (fm.statut) items.push(`📌 ${fm.statut}`);
-      if (fm.publish) items.push('✅ publié');
+      if (fm.publish) items.push('${t('graph.published_badge')}');
       if (fm.favoris) items.push('⭐ favoris');
       if (items.length > 0) fmSummary = `<div style="font-size:0.7rem;color:var(--text-muted);margin:4px 0">${items.join(' · ')}</div>`;
     }
@@ -764,7 +765,7 @@ export const GraphViewManager = {
       if (hit) {
         this._canvas.style.cursor = 'pointer';
         this._canvas.title = hit.node.type === 'file'
-          ? `📄 ${hit.node.name} (cliquer pour ouvrir${e.ctrlKey ? ', Ctrl+survol = aperçu' : ''})`
+          ? `📄 ${hit.node.name} (${t('graph.click_to_open')}${e.ctrlKey ? ', ${t('graph.ctrl_hover_preview_short')}' : ''})`
           : `📁 ${hit.node.name} (cliquer pour explorer)`;
         
         // Ctrl+hover: fetch content preview for file nodes