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/public.go

@@ -1,7 +1,9 @@
 package handler
 
 import (
+	"fmt"
 	"net/http"
+	"strings"
 
 	"github.com/gin-gonic/gin"
 	"gorm.io/gorm"
@@ -9,6 +11,12 @@ import (
 	"github.com/wangjia/jiu/backend/internal/model"
 )
 
+// 默认话术（保质期/储存方式空时使用）
+const (
+	defaultShelfLife = "无限期（适饮）"
+	defaultStorage   = "阴凉干燥、避光保存"
+)
+
 type PublicHandler struct {
 	db *gorm.DB
 }
@@ -24,6 +32,10 @@ func (h *PublicHandler) GetProduct(c *gin.Context) {
 	var product model.Product
 	if err := h.db.Where("public_id = ? AND deleted_at IS NULL", publicID).
 		Preload("Images").
+		Preload("Origin").
+		Preload("ShelfLife").
+		Preload("Storage").
+		Preload("DescriptionDoc").
 		First(&product).Error; err != nil {
 		c.JSON(http.StatusNotFound, gin.H{"error": "not found"})
 		return
@@ -60,22 +72,98 @@ func (h *PublicHandler) GetProduct(c *gin.Context) {
 		}
 	}
 
+	// 产地：空串表示无，前端不展示该行
+	origin := ""
+	if product.Origin != nil {
+		origin = product.Origin.Name
+	}
+
+	// 保质期：无关联时用默认话术
+	shelfLife := defaultShelfLife
+	if product.ShelfLife != nil {
+		shelfLife = product.ShelfLife.Name
+	}
+
+	// 储存方式：无关联时用默认话术
+	storage := defaultStorage
+	if product.Storage != nil {
+		storage = product.Storage.Name
+	}
+
+	// 介绍三级回退：描述文档 → 旧 Description → 通用中性兜底
+	descTitle, descBody, descKeywords := buildDescription(product)
+
 	c.JSON(http.StatusOK, gin.H{
 		"data": gin.H{
-			"id":          product.ID,
-			"name":        product.Name,
-			"series":      product.Series,
-			"spec":        product.Spec,
-			"brand":       product.Brand,
-			"unit":        product.Unit,
-			"description": product.Description,
-			"images":      product.Images,
-			"shop":        shopData,
-			"batch":       batchData,
+			"id":                product.ID,
+			"name":              product.Name,
+			"series":            product.Series,
+			"spec":              product.Spec,
+			"brand":             product.Brand,
+			"unit":              product.Unit,
+			"description":       descBody,
+			"description_title": descTitle,
+			"description_keywords": descKeywords,
+			"origin":            origin,
+			"shelf_life":        shelfLife,
+			"storage":           storage,
+			"images":            product.Images,
+			"shop":              shopData,
+			"batch":             batchData,
 		},
 	})
 }
 
+// buildDescription 商品介绍三级回退逻辑
+// 1. DescriptionDoc.Content（结构化介绍文档）
+// 2. Product.Description（旧自由文本）
+// 3. 通用中性兜底（用真实字段拼，不含品牌专属词）
+func buildDescription(p model.Product) (title, body string, keywords []string) {
+	// 1. 描述文档
+	if p.DescriptionDoc != nil && p.DescriptionDoc.Content != "" {
+		return p.DescriptionDoc.Title, p.DescriptionDoc.Content, buildKeywords(p)
+	}
+
+	// 2. 旧 Description 自由文本
+	if p.Description != "" {
+		return "商品介绍", p.Description, buildKeywords(p)
+	}
+
+	// 3. 通用中性兜底
+	parts := make([]string, 0, 4)
+	if p.Brand != "" && p.Name != "" {
+		parts = append(parts, fmt.Sprintf("%s%s", p.Brand, p.Name))
+	} else if p.Name != "" {
+		parts = append(parts, p.Name)
+	}
+	if p.Series != "" {
+		parts = append(parts, fmt.Sprintf("%s系列", p.Series))
+	}
+	if p.Spec != "" {
+		parts = append(parts, fmt.Sprintf("规格%s", p.Spec))
+	}
+	intro := strings.Join(parts, "，")
+	if intro != "" {
+		intro += "。"
+	}
+	intro += "本商品由门店正品供应，支持扫码验真，请认准官方渠道。"
+
+	return "商品介绍", intro, buildKeywords(p)
+}
+
+// buildKeywords 从真实商品属性派生关键词 chips
+func buildKeywords(p model.Product) []string {
+	kws := make([]string, 0, 4)
+	if p.Brand != "" {
+		kws = append(kws, p.Brand)
+	}
+	if p.Series != "" {
+		kws = append(kws, p.Series)
+	}
+	kws = append(kws, "正品保障", "扫码验真")
+	return kws
+}
+
 // GetRelease GET /api/v1/public/release (no auth)
 func (h *PublicHandler) GetRelease(c *gin.Context) {
 	cfg, err := loadVersionConfig()