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/handler/inventory.go

@@ -61,6 +61,7 @@ func (h *InventoryHandler) List(c *gin.Context) {
 
 	keyword := c.Query("keyword")
 	warehouseIDStr := c.Query("warehouse_id")
+	inStock := c.Query("in_stock")
 
 	if keyword != "" {
 		baseWhere += " AND (COALESCE(NULLIF(p.name,''), inv.product_name) LIKE ? OR COALESCE(NULLIF(p.code,''), inv.product_code) LIKE ?)"
@@ -71,6 +72,9 @@ func (h *InventoryHandler) List(c *gin.Context) {
 		baseWhere += " AND inv.warehouse_id = ?"
 		args = append(args, warehouseIDStr)
 	}
+	if inStock == "1" {
+		baseWhere += " AND inv.quantity > 0"
+	}
 
 	// Count query
 	countSQL := `
@@ -96,13 +100,13 @@ func (h *InventoryHandler) List(c *gin.Context) {
 		  COALESCE(NULLIF(p.unit,''), inv.unit, '') AS unit,
 		  COALESCE(NULLIF(w.name,''), inv.warehouse_name, '') AS warehouse_name,
 		  COALESCE(sii.unit_price, inv.unit_price) AS unit_price,
-		  COALESCE(DATE_FORMAT(sii.production_date,'%Y-%m-%d'), DATE_FORMAT(inv.production_date,'%Y-%m-%d')) AS production_date,
+		  COALESCE(DATE(sii.production_date), DATE(inv.production_date)) AS production_date,
 		  COALESCE(NULLIF(sii.batch_no,''), inv.batch_no, '') AS batch_no,
 		  inv.supplier_name,
 		  inv.remark,
 		  COALESCE(p.brand, '') AS brand,
 		  p.min_stock,
-		  DATE_FORMAT(inv.created_at, '%Y-%m-%dT%H:%i:%sZ') AS created_at
+		  inv.created_at
 		FROM inventories inv
 		LEFT JOIN stock_in_items sii ON sii.id = inv.stock_in_item_id
 		LEFT JOIN products p ON p.id = inv.product_id