refactor: remove Gorse integration and implement HotRank feature

- Removed Gorse-related configurations, handlers, and dependencies from the codebase.
- Introduced HotRank feature with configuration options for ranking posts based on recent activity.
- Updated application structure to support HotRank processing, including new caching mechanisms and database interactions.
- Cleaned up related DTOs and repository methods to reflect the removal of Gorse and the addition of HotRank functionality.

internal/cache/keys.go

@@ -9,6 +9,10 @@ const (
 	// 帖子相关
 	PrefixPostList = "posts:list"
 	PrefixPost     = "posts:detail"
+	// HotRankZSet 热门榜（有序集合，member=post_id，score=归一化热度，仅存 TopN）
+	HotRankZSet = "posts:hot:zset"
+	// HotRankTopIDs 热门榜有序 post_id 列表（JSON []string，供分层缓存本地层命中）
+	HotRankTopIDs = "posts:hot:top_ids"
 
 	// 会话相关
 	PrefixConversationList   = "conversations:list"
@@ -36,10 +40,20 @@ const (
 )
 
 // PostListKey 生成帖子列表缓存键
-// postType: 帖子类型 (recommend, hot, follow, latest)
+// postType: 帖子类型 (hot, follow, latest)
 // page: 页码
 // pageSize: 每页数量
 // userID: 用户维度（仅在个性化列表如 follow 场景使用）
+// HotRankZSetKey 热门榜 Redis ZSET 逻辑键（仅存 TopN，会经 normalizeKey 加前缀）
+func HotRankZSetKey() string {
+	return HotRankZSet
+}
+
+// HotRankTopIDsKey 热门榜 Top 顺序 ID 列表键（会经 normalizeKey 加前缀）
+func HotRankTopIDsKey() string {
+	return HotRankTopIDs
+}
+
 func PostListKey(postType string, userID string, page, pageSize int) string {
 	if userID == "" {
 		return fmt.Sprintf("%s:%s:%d:%d", PrefixPostList, postType, page, pageSize)