feat: Implement collection deletion and loading spinners

- Add API endpoint and handler to delete collections
- Introduce LoadingSpinner component for async operations
- Show loading spinners during file loading and preview rendering
- Enhance modal accessibility by removing aria-hidden attribute
- Refactor delete functionality to distinguish between collections and files/folders
- Remove unused collection definitions from config

config.yaml

@@ -8,18 +8,6 @@ collections:
   projects:
     path: ./collections/projects
     description: Project documentation
-  new_collectionss:
-    path: collections/new_collectionss
-    description: 'User-created collection: new_collectionss'
-  test_collection_new:
-    path: collections/test_collection_new
-    description: 'User-created collection: test_collection_new'
-  dynamic_test:
-    path: collections/dynamic_test
-    description: 'User-created collection: dynamic_test'
-  runtime_collection:
-    path: collections/runtime_collection
-    description: 'User-created collection: runtime_collection'
   7madah:
     path: collections/7madah
     description: 'User-created collection: 7madah'