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/widgets/chat_bubble.dart

@@ -9,6 +9,7 @@ import '../../../../share_intent/remote_file_ref.dart';
 import '../../../../state/app/modules/chat/bloc/chat_bloc.dart';
 import '../../../../utils/downloads/download_job.dart';
 import '../../../../utils/haptics.dart';
+import '../../../../widget/demo_restricted.dart';
 import '../../../../widget/downloads/download_trigger.dart';
 import '../data/chat_bubble_styles.dart';
 import '../data/chat_message.dart';
@@ -177,6 +178,7 @@ class _ChatBubbleState extends State<ChatBubble>
       return;
     }
     if (message.file == null) return;
+    if (guardDemoAction(context)) return;
     if (isDownloading) {
       confirmCancelDownload();
     } else {

lib/view/pages/talk/widgets/chat_bubble_reactions.dart

@@ -7,6 +7,7 @@ import '../../../../api/marianumcloud/talk/react_message/react_message.dart';
 import '../../../../api/marianumcloud/talk/react_message/react_message_params.dart';
 import '../../../../api/marianumcloud/talk/room/get_room_response.dart';
 import '../../../../widget/async_action_button.dart';
+import '../../../../widget/demo_restricted.dart';
 import '../../../../widget/emoji_text.dart';
 
 /// Reactions wrap shown beneath a chat bubble. Tapping a reaction toggles
@@ -60,6 +61,7 @@ class ChatBubbleReactions extends StatelessWidget {
                     ? Theme.of(context).primaryColor
                     : null,
                 onPressed: () {
+                  if (guardDemoAction(context)) return;
                   runWithErrorDialog(context, () async {
                     if (hasSelfReacted) {
                       await DeleteReactMessage(

lib/view/pages/talk/widgets/chat_message_options_dialog.dart

@@ -14,6 +14,7 @@ import '../../../../widget/app_progress_indicator.dart';
 import '../../../../widget/async_action_button.dart';
 import '../../../../widget/confirm_dialog.dart';
 import '../../../../widget/debug/debug_tile.dart';
+import '../../../../widget/demo_restricted.dart';
 import '../../../../widget/details_bottom_sheet.dart';
 import '../../../../widget/emoji_picker_dialog.dart';
 import '../../../../widget/emoji_text.dart';
@@ -64,6 +65,7 @@ void showChatMessageOptionsDialog(
           leading: const Icon(Icons.reply_outlined),
           title: const Text('Antworten'),
           onTap: () {
+            if (guardDemoAction(sheetCtx)) return;
             sheetCtx.read<ChatBloc>().setReferenceMessageId(bubbleData.id);
             Navigator.of(sheetCtx).pop();
           },
@@ -96,6 +98,7 @@ void showChatMessageOptionsDialog(
           leading: const Icon(Icons.cloud_outlined),
           title: const Text('In Cloud speichern'),
           onTap: () {
+            if (guardDemoAction(sheetCtx)) return;
             Navigator.of(sheetCtx).pop();
             if (!parentContext.mounted) return;
             AppRoutes.openInternalSaveToFolder(
@@ -109,6 +112,7 @@ void showChatMessageOptionsDialog(
           leading: const Icon(Icons.shortcut_outlined),
           title: const Text('Weiterleiten'),
           onTap: () {
+            if (guardDemoAction(sheetCtx)) return;
             Navigator.of(sheetCtx).pop();
             if (!parentContext.mounted) return;
             AppRoutes.openForwardMessageToChat(
@@ -143,6 +147,7 @@ void showChatMessageOptionsDialog(
           leading: const Icon(Icons.delete_outline),
           title: const Text('Nachricht löschen'),
           onTap: () {
+            if (guardDemoAction(sheetCtx)) return;
             ConfirmDialog(
               title: 'Nachricht löschen?',
               content: 'Die Nachricht wird für alle Teilnehmer gelöscht.',
@@ -189,6 +194,7 @@ class _ReactionsRowState extends State<_ReactionsRow> {
   }
 
   Future<void> _react(String emoji) async {
+    if (guardDemoAction(context)) return;
     final ok = await _controller.run(() async {
       await ReactMessage(
         chatToken: widget.chatToken,

lib/view/pages/talk/widgets/chat_textfield.dart

@@ -12,6 +12,7 @@ import '../../../../api/marianumcloud/webdav/webdav_api.dart';
 import '../../../../state/app/modules/chat/bloc/chat_bloc.dart';
 import '../../../../state/app/modules/settings/bloc/settings_cubit.dart';
 import '../../../../widget/async_action_button.dart';
+import '../../../../widget/demo_restricted.dart';
 import '../../../../widget/details_bottom_sheet.dart';
 import '../../../../widget/downloads/download_tray.dart';
 import '../../../../widget/emoji_picker_dialog.dart';
@@ -125,6 +126,7 @@ class _ChatTextfieldState extends State<ChatTextfield> {
   }
 
   void _showAttachmentSheet() {
+    if (guardDemoAction(context)) return;
     showDetailsBottomSheet(
       context,
       children: (sheetCtx) => [
@@ -187,6 +189,7 @@ class _ChatTextfieldState extends State<ChatTextfield> {
 
   Future<void> _sendMessage(ChatBloc chatBloc) async {
     if (_textBoxController.text.isEmpty) return;
+    if (guardDemoAction(context)) return;
     final text = _textBoxController.text;
     final replyTo = chatBloc.state.data?.referenceMessageId?.toString();
     final ownToken = widget.sendToToken;