feat(backend): 库存按商品过滤 + 香型(分类)字典 CRUD

商品域富数据/重组所需后端：
- GET /inventory 加 product_id 过滤 → 解锁商品详情「当前库存/货值/各仓库分布」
  （配合已支持 product_id 的 /inventory/logs，详情可拼出大半富数据）
- 新增 /product-options/categories 香型字典 CRUD（ProductCategory 模型已存在，
  补管理接口）→ 商品列表 5-tab 重组的最后一块字典
均守多租户 shop_id；新增 3 个测试（FilterByProduct/CategoryCRUD/CategoryIsolation）。
go build/vet/test 全过。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TSKEiHsvauyxYUW2itzUXX

backend/internal/handler/product_option.go

@@ -220,3 +220,68 @@ func (h *ProductOptionHandler) DeleteSpec(c *gin.Context) {
 	h.db.Where("id = ? AND shop_id = ?", c.Param("id"), shopID).Delete(&model.ProductSpecOption{})
 	c.JSON(http.StatusOK, gin.H{"message": "deleted"})
 }
+
+// ── 香型 / 分类（ProductCategory）字典 CRUD ──────────────────────────────
+
+func (h *ProductOptionHandler) ListCategories(c *gin.Context) {
+	shopID := middleware.GetShopID(c)
+	items := make([]model.ProductCategory, 0)
+	q := h.db.Where("shop_id = ?", shopID)
+	if kw := strings.TrimSpace(c.Query("keyword")); kw != "" {
+		q = q.Where("name LIKE ?", "%"+kw+"%")
+	}
+	q.Order("sort_order ASC, id ASC").Find(&items)
+	util.RespondSuccess(c, items)
+}
+
+func (h *ProductOptionHandler) CreateCategory(c *gin.Context) {
+	shopID := middleware.GetShopID(c)
+	var req struct {
+		Name      string  `json:"name" binding:"required"`
+		ParentID  *uint64 `json:"parent_id"`
+		SortOrder int     `json:"sort_order"`
+	}
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
+	item := model.ProductCategory{
+		TenantBase: model.TenantBase{ShopID: shopID},
+		Name:       req.Name,
+		ParentID:   req.ParentID,
+		SortOrder:  req.SortOrder,
+	}
+	if err := h.db.Create(&item).Error; err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+	util.RespondCreated(c, item)
+}
+
+func (h *ProductOptionHandler) UpdateCategory(c *gin.Context) {
+	shopID := middleware.GetShopID(c)
+	var req struct {
+		Name      string  `json:"name" binding:"required"`
+		ParentID  *uint64 `json:"parent_id"`
+		SortOrder int     `json:"sort_order"`
+	}
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
+	var item model.ProductCategory
+	if err := h.db.Where("id = ? AND shop_id = ?", c.Param("id"), shopID).First(&item).Error; err != nil {
+		c.JSON(http.StatusNotFound, gin.H{"error": "not found"})
+		return
+	}
+	h.db.Model(&item).Where("shop_id = ?", shopID).Updates(map[string]interface{}{
+		"name": req.Name, "parent_id": req.ParentID, "sort_order": req.SortOrder,
+	})
+	util.RespondSuccess(c, item)
+}
+
+func (h *ProductOptionHandler) DeleteCategory(c *gin.Context) {
+	shopID := middleware.GetShopID(c)
+	h.db.Where("id = ? AND shop_id = ?", c.Param("id"), shopID).Delete(&model.ProductCategory{})
+	c.JSON(http.StatusOK, gin.H{"message": "deleted"})
+}