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/timetable/data_provider/timetable_data_provider.dart

@@ -1,3 +1,5 @@
+import '../../../../../api/demo/data/demo_timetable.dart';
+import '../../../../../api/demo/demo_mode.dart';
 import '../../../../../api/marianumconnect/queries/timetable_get_holidays/timetable_get_holidays.dart';
 import '../../../../../api/marianumconnect/queries/timetable_get_holidays/timetable_get_holidays_response.dart';
 import '../../../../../api/marianumconnect/queries/timetable_get_rooms/timetable_get_rooms.dart';
@@ -95,27 +97,36 @@ class TimetableDataProvider {
   Future<GetCustomTimetableEventResponse> getCustomEvents({
     bool renew = false,
     void Function(Object)? onError,
-  }) => resolveFromCache<GetCustomTimetableEventResponse>(
+  }) {
+    if (DemoMode.active) return Future.value(DemoTimetable.customEvents());
+    return resolveFromCache<GetCustomTimetableEventResponse>(
     (onUpdate, onError) => GetCustomTimetableEventCache(
       GetCustomTimetableEventParams(AccountData().getUserSecret()),
       renew: renew,
       onUpdate: onUpdate,
       onError: onError,
     ),
-    onError: onError,
-    operationName: 'getCustomEvents',
-  );
+      onError: onError,
+      operationName: 'getCustomEvents',
+    );
+  }
 
-  Future<void> addCustomEvent(CustomTimetableEvent event) =>
-      AddCustomTimetableEvent(
-        AddCustomTimetableEventParams(AccountData().getUserSecret(), event),
-      ).run();
+  Future<void> addCustomEvent(CustomTimetableEvent event) {
+    if (DemoMode.active) return Future.value();
+    return AddCustomTimetableEvent(
+      AddCustomTimetableEventParams(AccountData().getUserSecret(), event),
+    ).run();
+  }
 
-  Future<void> updateCustomEvent(String id, CustomTimetableEvent event) =>
-      UpdateCustomTimetableEvent(
-        UpdateCustomTimetableEventParams(id, event),
-      ).run();
+  Future<void> updateCustomEvent(String id, CustomTimetableEvent event) {
+    if (DemoMode.active) return Future.value();
+    return UpdateCustomTimetableEvent(
+      UpdateCustomTimetableEventParams(id, event),
+    ).run();
+  }
 
-  Future<void> removeCustomEvent(String id) =>
-      RemoveCustomTimetableEvent(RemoveCustomTimetableEventParams(id)).run();
+  Future<void> removeCustomEvent(String id) {
+    if (DemoMode.active) return Future.value();
+    return RemoveCustomTimetableEvent(RemoveCustomTimetableEventParams(id)).run();
+  }
 }