feat(v1.3.0): Step 2 — DB tables collections, collection_pages, collection_views

- Ajout des 3 nouvelles tables pour le Database Concept
- collections: base de données abstraite, indépendante de Gitea
- collection_pages: pages génériques avec parent_id et property_values_json
- collection_views: vues configurables par collection
- Mise à jour test_db_tables_exist pour inclure les nouvelles tables
- 28/28 tests passent

app/templates/base.html

@@ -202,7 +202,7 @@
         <ul class="sidebar-items">
           <li class="sidebar-item" @click="navigateTo('/library')"><span class="page-icon">📚</span><span class="page-name">Library</span></li>
           <li class="sidebar-item"><span class="page-icon">✅</span><span class="page-name">My Tasks</span></li>
-          <li class="sidebar-item"><span class="page-icon">🗑️</span><span class="page-name">Trash</span></li>
+          <li class="sidebar-item" @click="navigateTo('/trash')"><span class="page-icon">🗑️</span><span class="page-name">Trash</span></li>
           <li class="sidebar-item"><span class="page-icon">❓</span><span class="page-name">Help</span></li>
         </ul>
       </div>