feat: #59 finalisation mode hors-ligne PWA — badge + conflits

- Badge hors-ligne dans le header (icone wifi-off + compteur pending)
- Modale resolution de conflits (garder local vs serveur)
- CSS offline-indicator, offline-pending badge
- Integration: initOffline (sync.js), cacheViewedFile (viewer.js), searchOffline (search.js)
- IndexedDB: files, content, pending stores avec sync queue
- ROADMAP: #59 marque FAIT

frontend/index.html

@@ -411,6 +411,13 @@
                 </div>
 
                 <div class="header-right">
+                    <!-- Offline indicator (hidden by default) -->
+                    <div
+                        class="header-icon offline-indicator"
+                        id="offline-badge"
+                        style="display:none"
+                        title="Mode hors-ligne"
+                    ></div>
                     <div
                         class="vault-context-indicator"
                         id="vault-context-indicator"
@@ -4738,5 +4745,22 @@ curl -X POST https://votre-serveur.com/webhook \
             <button class="results-bar-btn tog" id="rb-word" title="Mot entier (Alt-W)">wd</button>
             <button class="results-bar-btn tog" id="rb-regex" title="Expression reguliere (Alt-R)">.*</button>
         </div>
+        <!-- Offline conflict resolution modal -->
+        <div class="editor-modal" id="offline-conflict-modal">
+            <div class="editor-container" style="max-width:520px">
+                <div class="editor-header">
+                    <span class="editor-brand">Conflit hors-ligne</span>
+                    <div class="editor-spacer"></div>
+                    <button class="editor-btn" id="offline-conflict-close" title="Fermer" aria-label="Fermer">&#10005;</button>
+                </div>
+                <div class="editor-body" style="padding:20px;overflow:auto">
+                    <p style="color:var(--text-secondary);margin-bottom:12px" id="offline-conflict-msg"></p>
+                    <div style="display:flex;gap:8px">
+                        <button class="editor-btn primary" id="offline-conflict-keep-local">Garder ma version</button>
+                        <button class="editor-btn" id="offline-conflict-keep-server">Garder version serveur</button>
+                    </div>
+                </div>
+            </div>
+        </div>
     </body>
 </html>