implemented a comprehensive client-side demo mode triggered by a "demo@" username prefix, serving curated fixture data for all app modules

lib/state/app/modules/files/data_provider/files_data_provider.dart

@@ -1,5 +1,7 @@
 import 'package:nextcloud/nextcloud.dart';
 
+import '../../../../../api/demo/data/demo_files.dart';
+import '../../../../../api/demo/demo_mode.dart';
 import '../../../../../api/marianumcloud/webdav/queries/list_files/list_files_cache.dart';
 import '../../../../../api/marianumcloud/webdav/queries/list_files/list_files_response.dart';
 import '../../../../../api/marianumcloud/webdav/webdav_api.dart';
@@ -19,20 +21,24 @@ class FilesDataProvider {
     void Function(Object)? onError,
     bool renew = false,
     void Function(int nextAttempt, int maxAttempts)? onRetry,
-  }) => resolveFromCache<ListFilesResponse>(
-    (onUpdate, onError) => ListFilesCache(
-      path: path,
-      onUpdate: onUpdate,
-      onCacheData: onCacheData,
+  }) {
+    if (DemoMode.active) return Future.value(DemoFiles.listing(path));
+    return resolveFromCache<ListFilesResponse>(
+      (onUpdate, onError) => ListFilesCache(
+        path: path,
+        onUpdate: onUpdate,
+        onCacheData: onCacheData,
+        onError: onError,
+        renew: renew,
+        onRetry: onRetry,
+      ),
       onError: onError,
-      renew: renew,
-      onRetry: onRetry,
-    ),
-    onError: onError,
-    operationName: 'listFiles',
-  );
+      operationName: 'listFiles',
+    );
+  }
 
   Future<void> createFolder(String fullPath) async {
+    if (DemoMode.active) return;
     final webdav = await WebdavApi.webdav;
     await webdav.mkcol(PathUri.parse(fullPath));
   }