feat(api): add tab-based post feed endpoints with cursor pagination

Add support for different post feed types via tab parameter:
- follow: posts from followed users (requires authentication)
- hot: trending posts using Gorse most_liked_weekly or database fallback
- recommend: personalized recommendations with random offset for diversity
- latest: default chronological feed

The cursor pagination detection is also improved to check for parameter
existence rather than non-empty string value.

internal/handler/post_handler.go

@@ -147,8 +147,9 @@ func (h *PostHandler) RecordView(c *gin.Context) {
 // List 获取帖子列表（支持游标分页和偏移分页）
 func (h *PostHandler) List(c *gin.Context) {
 	// 检查是否使用游标分页
-	cursorStr := c.Query("cursor")
-	if cursorStr != "" {
+	// 当 cursor 参数存在时（包括空字符串），使用游标分页
+	_, cursorExists := c.GetQuery("cursor")
+	if cursorExists {
 		h.ListByCursor(c)
 		return
 	}
@@ -220,6 +221,7 @@ func (h *PostHandler) List(c *gin.Context) {
 func (h *PostHandler) ListByCursor(c *gin.Context) {
 	userID := c.Query("user_id")
 	currentUserID := c.GetString("user_id")
+	tab := c.Query("tab")
 
 	// 解析游标分页请求
 	req := h.parseCursorRequest(c)
@@ -227,8 +229,32 @@ func (h *PostHandler) ListByCursor(c *gin.Context) {
 	// 判断是否包含待审核帖子
 	includePending := userID != "" && userID == currentUserID
 
-	// 调用游标分页服务
-	result, err := h.postService.ListByCursor(c.Request.Context(), userID, includePending, req)
+	var result *cursor.CursorPageResult[*model.Post]
+	var err error
+
+	// 根据 tab 参数选择不同的获取方式
+	switch tab {
+	case "follow":
+		// 获取关注用户的帖子，需要登录
+		if currentUserID == "" {
+			response.Unauthorized(c, "请先登录")
+			return
+		}
+		result, err = h.postService.GetFollowingPostsByCursor(c.Request.Context(), currentUserID, req)
+	case "hot":
+		// 获取热门帖子
+		result, err = h.postService.GetHotPostsByCursor(c.Request.Context(), req)
+	case "recommend":
+		// 推荐帖子（从Gorse获取个性化推荐）
+		result, err = h.postService.GetRecommendedPostsByCursor(c.Request.Context(), currentUserID, req)
+	case "latest":
+		// 最新帖子
+		result, err = h.postService.ListByCursor(c.Request.Context(), userID, includePending, req)
+	default:
+		// 默认获取最新帖子
+		result, err = h.postService.ListByCursor(c.Request.Context(), userID, includePending, req)
+	}
+
 	if err != nil {
 		response.InternalServerError(c, "failed to get posts")
 		return