fix: permission error message and Android 13+ storage permission

- Fixed download showing 'Song not found' when actually permission error
- Added permission error type detection in Go backend
- Android 13+ now requests both MANAGE_EXTERNAL_STORAGE and READ_MEDIA_AUDIO
- MANAGE_EXTERNAL_STORAGE opens Settings (system-level)
- READ_MEDIA_AUDIO shows dialog (app-level, resets on clear data)
- Proper permission check before showing 'granted' status

lib/providers/download_queue_provider.dart

@@ -1677,6 +1677,9 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
           case 'network':
             errorType = DownloadErrorType.network;
             break;
+          case 'permission':
+            errorType = DownloadErrorType.permission;
+            break;
           default:
             errorType = DownloadErrorType.unknown;
         }