fix(test): 修复测试文件类型错误和测试数据库 schema 过期问题

- 修正 stock_in/out 测试中 WarehouseID/ProductID 指针误用（StockOrder 用 uint64，Inventory 用 *uint64）
- 更新 testutil/setup.go：inventories 表加入所有批次字段，stock_in_items 加 production_date，新增 finance_records 表
- 修正 inventory handler 中 DATE_FORMAT（MySQL 专属）→ DATE()（跨 DB 兼容）
- 更新断言：order_no 前缀改为 RK，库存总量用 SUM 替代 First
- 库存 List 新增 in_stock=1 过滤器

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/internal/service/stock_test.go

@@ -98,8 +98,8 @@ func TestStockService_ApproveStockOut_Success(t *testing.T) {
 	// 先入库
 	inv := model.Inventory{
 		ShopID:     shop.ID,
-		WarehouseID: warehouse.ID,
-		ProductID:   product.ID,
+		WarehouseID: &warehouse.ID,
+		ProductID:   &product.ID,
 		Quantity:    20,
 	}
 	require.NoError(t, db.Create(&inv).Error)
@@ -149,8 +149,8 @@ func TestStockService_ApproveStockOut_InsufficientStock(t *testing.T) {
 	// 库存只有 3
 	inv := model.Inventory{
 		ShopID:     shop.ID,
-		WarehouseID: warehouse.ID,
-		ProductID:   product.ID,
+		WarehouseID: &warehouse.ID,
+		ProductID:   &product.ID,
 		Quantity:    3,
 	}
 	require.NoError(t, db.Create(&inv).Error)
@@ -207,7 +207,7 @@ func TestStockService_ApproveStockOut_ProductNotInInventory(t *testing.T) {
 	svc := NewStockService(db)
 	err := svc.ApproveStockOut(shop.ID, order.ID, user.ID)
 	assert.Error(t, err)
-	assert.Contains(t, err.Error(), "not in inventory")
+	assert.ErrorIs(t, err, ErrInsufficientStock)
 }
 
 func TestStockService_GenerateOrderNo(t *testing.T) {
@@ -219,7 +219,7 @@ func TestStockService_GenerateOrderNo(t *testing.T) {
 	require.NoError(t, err)
 	assert.NotEmpty(t, no)
 	// 单号格式: prefix + date + 6位序号
-	assert.Contains(t, no, "st")
+	assert.Contains(t, no, "RK")
 
 	// 第二次生成序号应递增
 	no2, err := svc.GenerateOrderNo(shop.ID, "stock_in")
@@ -288,9 +288,11 @@ func TestStockService_MultipleStockIn_AccumulatesInventory(t *testing.T) {
 	require.NoError(t, db.Create(&order2).Error)
 	require.NoError(t, svc.ApproveStockIn(shop.ID, order2.ID, user.ID))
 
-	// 总库存应该是 15
-	var inv model.Inventory
-	db.Where("shop_id = ? AND warehouse_id = ? AND product_id = ?",
-		shop.ID, warehouse.ID, product.ID).First(&inv)
-	assert.Equal(t, float64(15), inv.Quantity)
+	// 总库存应该是 15（两个批次之和）
+	var totalQty float64
+	db.Model(&model.Inventory{}).
+		Where("shop_id = ? AND warehouse_id = ? AND product_id = ? AND deleted_at IS NULL",
+			shop.ID, &warehouse.ID, &product.ID).
+		Select("COALESCE(SUM(quantity), 0)").Scan(&totalQty)
+	assert.Equal(t, float64(15), totalQty)
 }