feat(backend): 入库每行新建独立产品发独立序列号(product 加生产日期/批次列)

入库 Create/Update 改为对每条明细新建独立 product（createIndependentProduct，
nextProductCode 自增 + uk_shop_code 唯一约束兜底），回填 product_id；不再按名称复用。
product 表加 production_date/batch_no。向后兼容：保留明细/库存快照列。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YZ4DskSRKsSiheQonFtQvx

backend/internal/handler/stock_in.go

@@ -106,19 +106,28 @@ func (h *StockInHandler) Create(c *gin.Context) {
 	}
 	req.OrderNo = orderNo
 
-	// 计算总金额；自动生成批次号
-	var total float64
-	for i := range req.Items {
-		req.Items[i].ShopID = shopID
-		req.Items[i].TotalPrice = req.Items[i].Quantity * req.Items[i].UnitPrice
-		total += req.Items[i].TotalPrice
-		if req.Items[i].BatchNo == "" {
-			req.Items[i].BatchNo = fmt.Sprintf("%s-%02d", req.OrderNo, i+1)
+	// 事务内：每条明细新建一个独立产品（特有产品/序列号，不按名称复用），回填 product_id，再建单。
+	err = h.db.Transaction(func(tx *gorm.DB) error {
+		var total float64
+		for i := range req.Items {
+			it := &req.Items[i]
+			it.ShopID = shopID
+			if it.BatchNo == "" {
+				it.BatchNo = fmt.Sprintf("%s-%02d", req.OrderNo, i+1)
+			}
+			prod, e := createIndependentProduct(tx, shopID, it.ProductName, it.Series, it.Spec, it.BatchNo, it.ProductionDate, it.UnitPrice)
+			if e != nil {
+				return e
+			}
+			it.ProductID = prod.ID
+			it.ProductCode = prod.Code // 保留快照,兼容现有查询(瘦身阶段再去)
+			it.TotalPrice = it.Quantity * it.UnitPrice
+			total += it.TotalPrice
 		}
-	}
-	req.TotalAmount = total
-
-	if err := h.db.Create(&req).Error; err != nil {
+		req.TotalAmount = total
+		return tx.Create(&req).Error
+	})
+	if err != nil {
 		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
 		return
 	}
@@ -148,13 +157,20 @@ func (h *StockInHandler) Update(c *gin.Context) {
 		}
 		var total float64
 		for i := range req.Items {
-			req.Items[i].ShopID = shopID
-			req.Items[i].OrderID = order.ID
-			req.Items[i].TotalPrice = req.Items[i].Quantity * req.Items[i].UnitPrice
-			total += req.Items[i].TotalPrice
-			if req.Items[i].BatchNo == "" {
-				req.Items[i].BatchNo = fmt.Sprintf("%s-%02d", order.OrderNo, i+1)
+			it := &req.Items[i]
+			it.ShopID = shopID
+			it.OrderID = order.ID
+			if it.BatchNo == "" {
+				it.BatchNo = fmt.Sprintf("%s-%02d", order.OrderNo, i+1)
 			}
+			// 编辑草稿:旧明细已删,每条按新模型重建独立产品（旧草稿 product 无库存,暂留待后续清理）
+			prod, e := createIndependentProduct(tx, shopID, it.ProductName, it.Series, it.Spec, it.BatchNo, it.ProductionDate, it.UnitPrice)
+			if e != nil {
+				return e
+			}
+			it.ProductID = prod.ID
+			it.ProductCode = prod.Code
+			it.TotalPrice = it.Quantity * it.UnitPrice
 		}
 		updates := map[string]interface{}{
 			"warehouse_id": req.WarehouseID,