Fix error handling in file explorer by updating DioError to DioException for improved error message extraction

b0esche_cloud/lib/pages/file_explorer.dart

@@ -342,7 +342,7 @@ class _FileExplorerState extends State<FileExplorer> {
       snackController.close();
       String errorMsg = e.toString();
       // If DioError, try to extract backend error message
-      if (e is DioError) {
+      if (e is DioException) {
         final data = e.response?.data;
         if (data is Map && data.containsKey('message')) {
           errorMsg = data['message'].toString();