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/nextcloud_capabilities/bloc/nextcloud_capabilities_cubit.dart

@@ -2,6 +2,8 @@ import 'dart:developer';
 
 import 'package:hydrated_bloc/hydrated_bloc.dart';
 
+import '../../../../../api/demo/data/demo_capabilities.dart';
+import '../../../../../api/demo/demo_mode.dart';
 import '../../../../../api/marianumcloud/capabilities/get_nextcloud_capabilities.dart';
 import 'nextcloud_capabilities_state.dart';
 
@@ -57,6 +59,10 @@ class NextcloudCapabilitiesCubit
   /// Refreshes capabilities from the server. On any failure the previously
   /// hydrated flags are kept but the state is marked `loaded`.
   Future<void> load() async {
+    if (DemoMode.active) {
+      emit(DemoNextcloudCapabilities.state());
+      return;
+    }
     try {
       final caps = await GetNextcloudCapabilities().run();
       emit(