feat: expose hasAnyLocalData on DataImportUseCase

Thin pass-through to the existing LocalDataBackupRepository.hasAnyUserData()
port, needed by F2 to decide whether the import confirmation can be
simplified per UX cadrage (#84) when the device has no local data yet.

lib/application/use_cases.dart

@@ -188,6 +188,8 @@ final class DataImportUseCase {
     return codec.preview(bytes);
   }
 
+  Future<bool> hasAnyLocalData() => repository.hasAnyUserData();
+
   Future<LocalBackupImportResult> importFrom(
     Uint8List bytes, {
     required LocalBackupImportMode mode,