feat(listings): 足迹与收藏改为账号同步并新增后端表与接口

backend/internal/model/listing_collection.go

@@ -0,0 +1,24 @@
+package model
+
+import "time"
+
+const (
+	ListingCollectionKindHistory  = "history"
+	ListingCollectionKindFavorite = "favorite"
+)
+
+// ListingCollection 记录用户对商品的浏览足迹或收藏关系。
+// 同一用户 + 商品 + 类型唯一，重复浏览只更新时间，不新增行。
+type ListingCollection struct {
+	ID         uint64    `gorm:"primaryKey" json:"id"`
+	UserID     uint64    `gorm:"not null;uniqueIndex:uk_listing_collections_user_listing_kind,priority:1;index:idx_listing_collections_user_kind_time,priority:1" json:"user_id"`
+	ListingID  uint64    `gorm:"not null;uniqueIndex:uk_listing_collections_user_listing_kind,priority:2;index:idx_listing_collections_user_kind_time,priority:3;index:idx_listing_collections_listing" json:"listing_id"`
+	Kind       string    `gorm:"size:16;not null;uniqueIndex:uk_listing_collections_user_listing_kind,priority:3;index:idx_listing_collections_user_kind_time,priority:2" json:"kind"`
+	OccurredAt time.Time `gorm:"not null;index:idx_listing_collections_user_kind_time,priority:4" json:"occurred_at"`
+	CreatedAt  time.Time `json:"created_at"`
+	UpdatedAt  time.Time `json:"updated_at"`
+}
+
+func (ListingCollection) TableName() string {
+	return "listing_collections"
+}