결재 API 계약 보완 및 테스트 정리

lib/features/masters/vendor/data/repositories/vendor_repository_remote.dart

@@ -50,9 +50,10 @@ class VendorRepositoryRemote implements VendorRepository {
 
   @override
   Future<Vendor> update(int id, VendorInput input) async {
+    final payload = vendorInputToJson(input)..['id'] = id;
     final response = await _api.patch<Map<String, dynamic>>(
       '$_basePath/$id',
-      data: vendorInputToJson(input),
+      data: payload,
       options: Options(responseType: ResponseType.json),
     );
     final data = (response.data?['data'] as Map<String, dynamic>?) ?? {};