결재 API 계약 보완 및 테스트 정리

lib/features/masters/customer/data/repositories/customer_repository_remote.dart

@@ -66,9 +66,10 @@ class CustomerRepositoryRemote implements CustomerRepository {
   /// 고객 정보를 수정한다.
   @override
   Future<Customer> update(int id, CustomerInput input) async {
+    final payload = customerInputToJson(input)..['id'] = id;
     final response = await _api.patch<Map<String, dynamic>>(
       '$_basePath/$id',
-      data: customerInputToJson(input),
+      data: payload,
       options: Options(responseType: ResponseType.json),
     );
     final data = (response.data?['data'] as Map<String, dynamic>?) ?? {};