fix: 批量修复功能问题 - 购物车结算/订单库存积分/搜索/抽奖/个人资料等

backend/internal/models/category.go

@@ -21,6 +21,7 @@ type Category struct {
 	CreatedAt    time.Time      `json:"created_at"`
 	UpdatedAt    time.Time      `json:"updated_at"`
 	DeletedAt    gorm.DeletedAt `gorm:"index" json:"-"`
+	ProductCount int64          `gorm:"-" json:"product_count"`
 	Children     []Category     `gorm:"foreignKey:ParentID" json:"children,omitempty"`
 }