implemented comprehensive accessibility (A11y) support across the app

lib/view/pages/files/search/files_search_delegate.dart

@@ -33,6 +33,7 @@ class FilesSearchDelegate extends SearchDelegate<void> {
   @override
   Widget? buildLeading(BuildContext context) => IconButton(
     icon: const Icon(Icons.arrow_back),
+    tooltip: 'Zurück',
     onPressed: () => close(context, null),
   );