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

lib/view/pages/timetable/custom_events/custom_event_edit_dialog.dart

@@ -10,6 +10,7 @@ import '../../../../api/mhsl/custom_timetable_event/custom_timetable_event.dart'
 import '../../../../extensions/date_time.dart';
 import '../../../../state/app/modules/timetable/bloc/timetable_bloc.dart';
 import '../../../../widget/async_action_button.dart';
+import '../../../../widget/demo_restricted.dart';
 import '../../../../widget/focus_behaviour.dart';
 import 'custom_event_colors.dart';
 
@@ -130,6 +131,7 @@ class _CustomEventEditDialogState extends State<CustomEventEditDialog> {
       end.second == 0;
 
   Future<void> _save() async {
+    if (guardDemoAction(context)) return;
     if (_name.text.trim().isEmpty) {
       throw Exception('Bitte einen Terminnamen eingeben.');
     }

lib/view/pages/timetable/details/delete_custom_event.dart

@@ -6,12 +6,14 @@ import 'package:flutter_bloc/flutter_bloc.dart';
 import '../../../../api/mhsl/custom_timetable_event/custom_timetable_event.dart';
 import '../../../../state/app/modules/timetable/bloc/timetable_bloc.dart';
 import '../../../../widget/confirm_dialog.dart';
+import '../../../../widget/demo_restricted.dart';
 
 Completer<void> showDeleteCustomEventDialog(
   BuildContext context,
   CustomTimetableEvent event,
 ) {
   final completer = Completer<void>();
+  if (guardDemoAction(context)) return completer;
   final bloc = context.read<TimetableBloc>();
   ConfirmDialog(
     title: 'Termin löschen',

lib/view/pages/timetable/timetable.dart

@@ -11,6 +11,7 @@ import '../../../state/app/modules/settings/bloc/settings_cubit.dart';
 import '../../../state/app/modules/timetable/bloc/timetable_bloc.dart';
 import '../../../state/app/modules/timetable/bloc/timetable_state.dart';
 import '../../../utils/haptics.dart';
+import '../../../widget/demo_restricted.dart';
 import 'custom_events/custom_event_edit_dialog.dart';
 import 'details/appointment_details_dispatcher.dart';
 import 'widgets/timetable_calendar_view.dart';
@@ -42,6 +43,7 @@ class _TimetableState extends State<Timetable> {
       state.startDate == _mondayOf(_initialDisplayDate());
 
   Future<void> _openPicker() async {
+    if (guardDemoAction(context)) return;
     final ref = await AppRoutes.openElementPicker(context);
     if (!mounted || ref == null) return;
     setState(() => _selected = ref);