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

lib/view/pages/talk/data/open_direct_chat.dart

@@ -5,6 +5,7 @@ import '../../../../api/marianumcloud/talk/room/get_room_response.dart';
 import '../../../../routing/app_routes.dart';
 import '../../../../state/app/modules/chat_list/bloc/chat_list_bloc.dart';
 import '../../../../widget/confirm_dialog.dart';
+import '../../../../widget/demo_restricted.dart';
 
 /// Opens an existing 1:1 chat with [actorId] or, after confirmation, creates
 /// one. Shared between the group-message context menu and the reactions
@@ -14,6 +15,7 @@ void openOrCreateDirectChat(
   required String actorId,
   required String actorDisplayName,
 }) {
+  if (guardDemoAction(context)) return;
   final chatListBloc = context.read<ChatListBloc>();
 
   GetRoomResponseObject? findExisting() {