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

lib/view/pages/files/widgets/file_element.dart

@@ -15,6 +15,7 @@ import '../../../../utils/file_clipboard.dart';
 import '../../../../utils/haptics.dart';
 import '../../../../widget/centered_leading.dart';
 import '../../../../widget/confirm_dialog.dart';
+import '../../../../widget/demo_restricted.dart';
 import '../../../../widget/details_bottom_sheet.dart';
 import '../../../../widget/downloads/download_trigger.dart';
 import '../../../../widget/info_dialog.dart';
@@ -105,6 +106,7 @@ class _FileElementState extends State<FileElement>
       );
       return;
     }
+    if (guardDemoAction(context)) return;
     if (EndpointData().getEndpointMode() == EndpointMode.stage) {
       InfoDialog.show(
         context,
@@ -135,6 +137,7 @@ class _FileElementState extends State<FileElement>
       isDirectory ? '$folder$name/' : '$folder$name';
 
   Future<void> _rename() async {
+    if (guardDemoAction(context)) return;
     final controller = TextEditingController(text: widget.file.name);
     try {
       final newName = await showDialog<String>(
@@ -182,6 +185,7 @@ class _FileElementState extends State<FileElement>
   }
 
   void _putOnClipboard({required bool copy}) {
+    if (guardDemoAction(context)) return;
     if (copy) {
       FileClipboard.instance.copy([widget.file]);
     } else {
@@ -198,6 +202,7 @@ class _FileElementState extends State<FileElement>
   }
 
   Future<void> _delete() async {
+    if (guardDemoAction(context)) return;
     await showDialog<void>(
       context: context,
       builder: (context) => ConfirmDialog(
@@ -269,6 +274,7 @@ class _FileElementState extends State<FileElement>
             title: const Text('Im Talk-Chat versenden'),
             onTap: () {
               Navigator.of(sheetCtx).pop();
+              if (guardDemoAction(context)) return;
               AppRoutes.openInternalShareToChat(
                 context,
                 RemoteFileRef.fromCacheable(widget.file),