fix: translate dashboard tabs, header menu items

- showWelcome() dashboard: all tabs, empty states, hints → ${t()}
- Header dropdown: 7 menu items with data-i18n (Thème..Déconnexion)
- 61 new locale keys for dashboard, settings nav, help nav, about
- Total: 658 keys per language

frontend/js/viewer.js

@@ -933,23 +933,23 @@ export function showWelcome() {
         <!-- Dashboard Tabs -->
         <div class="dashboard-tabs">
           <button class="dashboard-tab active" data-tab="stats">
-            <i data-lucide="bar-chart-3" style="width:14px;height:14px"></i> Statistiques
+            <i data-lucide="bar-chart-3" style="width:14px;height:14px"></i> ${t('dashboard.stats')}
           </button>
           <button class="dashboard-tab" data-tab="bookmarks">
-            <i data-lucide="bookmark" style="width:14px;height:14px"></i> Bookmarks
+            <i data-lucide="bookmark" style="width:14px;height:14px"></i> ${t('dashboard.bookmarks')}
           </button>
           <button class="dashboard-tab" data-tab="recent">
-            <i data-lucide="clock" style="width:14px;height:14px"></i> Récents
+            <i data-lucide="clock" style="width:14px;height:14px"></i> ${t('dashboard.tab_recent')}
           </button>
           <button class="dashboard-tab" data-tab="shared">
-            <i data-lucide="share-2" style="width:14px;height:14px"></i> Partagés
+            <i data-lucide="share-2" style="width:14px;height:14px"></i> ${t('dashboard.tab_shared')}
           </button>
         </div>
 
         <!-- Stats Panel -->
         <div id="dashboard-panel-stats" class="dashboard-panel active">
           <div id="dashboard-stats-grid" class="dashboard-stats-grid">
-            <div class="dashboard-stats-loading">Chargement...</div>
+            <div class="dashboard-stats-loading">${t('common.loading')}</div>
           </div>
           <div id="dashboard-conflicts-container" style="margin-top:16px"></div>
         </div>
@@ -959,8 +959,8 @@ export function showWelcome() {
           <div id="dashboard-bookmarks-grid" class="dashboard-recent-grid"></div>
           <div id="dashboard-bookmarks-empty" class="dashboard-recent-empty">
             <i data-lucide="pin"></i>
-            <span>Aucun bookmark</span>
-            <p>Épinglez des fichiers pour les retrouver ici.</p>
+            <span>${t('dashboard.no_bookmarks')}</span>
+            <p>${t('dashboard.pin_hint')}</p>
           </div>
         </div>
 
@@ -978,8 +978,8 @@ export function showWelcome() {
           </div>
           <div id="dashboard-recent-empty" class="dashboard-recent-empty hidden">
             <i data-lucide="inbox"></i>
-            <span>Aucun fichier récent</span>
-            <p>Ouvrez un fichier pour le voir apparaître ici</p>
+            <span>${t('dashboard.no_recent')}</span>
+            <p>${t('dashboard.recent_hint')}</p>
           </div>
         </div>
 
@@ -988,8 +988,8 @@ export function showWelcome() {
           <div id="dashboard-shared-grid" class="dashboard-recent-grid"></div>
           <div id="dashboard-shared-empty" class="dashboard-recent-empty">
             <i data-lucide="share-2"></i>
-            <span>Aucun document partagé</span>
-            <p>Partagez un document pour le voir apparaître ici</p>
+            <span>${t('dashboard.no_shares')}</span>
+            <p>${t('dashboard.shared_hint')}</p>
           </div>
         </div>
       </div>`;