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/sharing/share_sheet.dart

@@ -13,6 +13,7 @@ import '../../../../state/app/modules/nextcloud_capabilities/bloc/nextcloud_capa
 import '../../../../utils/clipboard_helper.dart';
 import '../../../../widget/app_progress_indicator.dart';
 import '../../../../widget/centered_leading.dart';
+import '../../../../widget/demo_restricted.dart';
 import '../../../../widget/details_bottom_sheet.dart';
 import '../../../../widget/info_dialog.dart';
 import '../widgets/file_leading.dart';
@@ -23,6 +24,7 @@ import 'share_password_sheet.dart';
 /// gated actions to create new ones (public link, user/group). Capability
 /// gating mirrors the Nextcloud web UI.
 void showShareSheet(BuildContext context, CacheableFile file) {
+  if (guardDemoAction(context)) return;
   showDetailsBottomSheet(
     context,
     header: ListTile(