번호 자동 부여 대응 및 API 공통 처리 보강

integration_test/stock_transaction_state_flow_test.dart

@@ -183,10 +183,10 @@ class _FakeStockTransactionRepository implements StockTransactionRepository {
   @override
   Future<StockTransaction> create(StockTransactionCreateInput input) async {
     final id = _sequence++;
+    final generatedNo = 'FAKE-${id.toString().padLeft(6, '0')}';
     final transaction = StockTransaction(
       id: id,
-      transactionNo:
-          input.transactionNo ?? 'FAKE-${id.toString().padLeft(6, '0')}',
+      transactionNo: generatedNo,
       transactionDate: input.transactionDate,
       type: StockTransactionType(id: input.transactionTypeId, name: '테스트 트랜잭션'),
       status: StockTransactionStatus(id: initialStatusId, name: '작성중'),