feat: add folder-based recipe organization and navigation

- Add new API endpoints for folder operations: get_folders, get_folder_tree, and get_unified_folder_tree
- Extend recipe listing handler to support folder and recursive filtering parameters
- Register new folder-related routes in route definitions
- Enable users to organize and browse recipes using folder structures

templates/recipes.html

@@ -75,7 +75,9 @@
           </div>
         </div>
     </div>
-    
+
+    {% include 'components/folder_sidebar.html' %}
+
     <!-- Recipe grid -->
     <div class="card-grid" id="recipeGrid">
         <!-- Remove the server-side conditional rendering and placeholder -->