feat(backend): 新增商品属性字典表（产地/保质期/储存方式/描述文档）

- model/product_attr.go: 新增 4 张字典表 struct（TenantBase 范式）
- model/product.go: Product 增加 4 个可空外键 + belongs-to 关联
- handler/product_attr.go: 4 组 16 个 CRUD handler（shop_id 隔离）
- handler/product.go: FindOrCreate/Update 支持写入 4 个属性 ID
- handler/public.go: Preload 4 表 + 三级回退介绍 + 默认话术常量
- router/router.go: /product-options/{origins,shelf-lives,storages,description-docs} 路由
- main.go: AutoMigrate 注册 4 个新 model
- testutil/setup.go: SQLite 测试库补齐新列与新表

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

backend/internal/handler/product.go

@@ -127,22 +127,26 @@ func (h *ProductHandler) Update(c *gin.Context) {
 	namePinyin, nameInitials := util.ToPinyin(req.Name)
 	// 只更新业务字段，防止 Save() 覆盖 shop_id / created_at 等系统字段
 	if err := h.db.Model(&product).Updates(map[string]interface{}{
-		"code":           req.Code,
-		"barcode":        req.Barcode,
-		"name":           req.Name,
-		"series":         req.Series,
-		"spec":           req.Spec,
-		"unit":           req.Unit,
-		"category_id":    req.CategoryID,
-		"brand":          req.Brand,
-		"purchase_price": req.PurchasePrice,
-		"sale_price":     req.SalePrice,
-		"min_stock":      req.MinStock,
-		"description":    req.Description,
-		"remark":         req.Remark,
-		"custom_fields":  req.CustomFields,
-		"name_pinyin":    namePinyin,
-		"name_initials":  nameInitials,
+		"code":               req.Code,
+		"barcode":            req.Barcode,
+		"name":               req.Name,
+		"series":             req.Series,
+		"spec":               req.Spec,
+		"unit":               req.Unit,
+		"category_id":        req.CategoryID,
+		"brand":              req.Brand,
+		"purchase_price":     req.PurchasePrice,
+		"sale_price":         req.SalePrice,
+		"min_stock":          req.MinStock,
+		"description":        req.Description,
+		"remark":             req.Remark,
+		"custom_fields":      req.CustomFields,
+		"name_pinyin":        namePinyin,
+		"name_initials":      nameInitials,
+		"origin_id":          req.OriginID,
+		"shelf_life_id":      req.ShelfLifeID,
+		"storage_id":         req.StorageID,
+		"description_doc_id": req.DescriptionDocID,
 	}).Error; err != nil {
 		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
 		return
@@ -208,9 +212,13 @@ func (h *ProductHandler) QRCode(c *gin.Context) {
 func (h *ProductHandler) FindOrCreate(c *gin.Context) {
 	shopID := middleware.GetShopID(c)
 	var req struct {
-		Name   string `json:"name" binding:"required"`
-		Series string `json:"series"`
-		Spec   string `json:"spec"`
+		Name             string  `json:"name" binding:"required"`
+		Series           string  `json:"series"`
+		Spec             string  `json:"spec"`
+		OriginID         *uint64 `json:"origin_id"`
+		ShelfLifeID      *uint64 `json:"shelf_life_id"`
+		StorageID        *uint64 `json:"storage_id"`
+		DescriptionDocID *uint64 `json:"description_doc_id"`
 	}
 	if err := c.ShouldBindJSON(&req); err != nil {
 		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
@@ -221,6 +229,23 @@ func (h *ProductHandler) FindOrCreate(c *gin.Context) {
 	err := h.db.Where("shop_id = ? AND name = ? AND series = ? AND spec = ? AND deleted_at IS NULL",
 		shopID, req.Name, req.Series, req.Spec).First(&product).Error
 	if err == nil {
+		// 商品已存在：如果传入了属性 ID，则更新属性关联
+		attrUpdates := map[string]interface{}{}
+		if req.OriginID != nil {
+			attrUpdates["origin_id"] = req.OriginID
+		}
+		if req.ShelfLifeID != nil {
+			attrUpdates["shelf_life_id"] = req.ShelfLifeID
+		}
+		if req.StorageID != nil {
+			attrUpdates["storage_id"] = req.StorageID
+		}
+		if req.DescriptionDocID != nil {
+			attrUpdates["description_doc_id"] = req.DescriptionDocID
+		}
+		if len(attrUpdates) > 0 {
+			h.db.Model(&product).Updates(attrUpdates)
+		}
 		c.JSON(http.StatusOK, gin.H{"data": product})
 		return
 	}
@@ -233,14 +258,18 @@ func (h *ProductHandler) FindOrCreate(c *gin.Context) {
 	h.db.Model(&model.Product{}).Where("shop_id = ? AND deleted_at IS NULL", shopID).Count(&count)
 	namePinyin, nameInitials := util.ToPinyin(req.Name)
 	product = model.Product{
-		TenantBase:   model.TenantBase{ShopID: shopID},
-		PublicID:     uuid.New().String(),
-		Name:         req.Name,
-		Series:       req.Series,
-		Spec:         req.Spec,
-		Code:         fmt.Sprintf("P%03d", count+1),
-		NamePinyin:   namePinyin,
-		NameInitials: nameInitials,
+		TenantBase:       model.TenantBase{ShopID: shopID},
+		PublicID:         uuid.New().String(),
+		Name:             req.Name,
+		Series:           req.Series,
+		Spec:             req.Spec,
+		Code:             fmt.Sprintf("P%03d", count+1),
+		NamePinyin:       namePinyin,
+		NameInitials:     nameInitials,
+		OriginID:         req.OriginID,
+		ShelfLifeID:      req.ShelfLifeID,
+		StorageID:        req.StorageID,
+		DescriptionDocID: req.DescriptionDocID,
 	}
 	if createErr := h.db.Create(&product).Error; createErr != nil {
 		// Race condition: try to find the record created by another request