feat : add Gitea tab to admin page

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/pages/admin.vue

@@ -25,6 +25,7 @@
             <AdminPriorityTab v-if="activeTab === 'priorities'" />
             <AdminTagTab v-if="activeTab === 'tags'" />
             <AdminUserTab v-if="activeTab === 'users'" />
+            <AdminGiteaTab v-if="activeTab === 'gitea'" />
         </div>
     </div>
 </template>
@@ -39,6 +40,7 @@ const tabs = [
     { key: 'priorities', label: 'Priorités' },
     { key: 'tags', label: 'Tags' },
     { key: 'users', label: 'Utilisateurs' },
+    { key: 'gitea', label: 'Gitea' },
 ] as const
 
 type TabKey = typeof tabs[number]['key']