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/repository/post_repo.go

@@ -906,3 +906,113 @@ func (r *PostRepository) GetUserPostsByCursor(ctx context.Context, userID string
 
 	return cursor.NewCursorPageResult(posts, nextCursor, prevCursor, hasMore), nil
 }
+
+// GetFollowingPostsByCursor 游标分页获取关注用户的帖子
+func (r *PostRepository) GetFollowingPostsByCursor(ctx context.Context, userID string, req *cursor.PageRequest) (*cursor.CursorPageResult[*model.Post], error) {
+	db := r.getDB(ctx).WithContext(ctx)
+
+	// 子查询：获取当前用户关注的所有用户ID
+	subQuery := db.Model(&model.Follow{}).Where("follower_id = ?", userID).Select("following_id")
+
+	// 构建基础查询
+	query := db.Model(&model.Post{}).Where("user_id IN (?) AND status = ?", subQuery, model.PostStatusPublished)
+
+	// 使用游标构建器
+	builder := cursor.NewBuilder(query, cursor.SortByCreatedAtDesc).
+		WithCursor(req.Cursor, req.Direction).
+		WithPageSize(req.PageSize)
+
+	if builder.Error() != nil {
+		// 无效游标，返回空列表
+		return cursor.NewCursorPageResult[*model.Post]([]*model.Post{}, "", "", false), nil
+	}
+
+	// 执行查询
+	var posts []*model.Post
+	query = builder.Build().Preload("User").Preload("Images")
+	if err := query.Find(&posts).Error; err != nil {
+		return nil, err
+	}
+
+	// 构建响应
+	pageSize := builder.GetPageSize()
+	hasMore := cursor.HasMore(len(posts), pageSize)
+	if hasMore {
+		posts = posts[:pageSize]
+	}
+
+	// 生成游标
+	var nextCursor, prevCursor string
+	if len(posts) > 0 {
+		if hasMore {
+			lastPost := posts[len(posts)-1]
+			nextCursor = cursor.NewCursor(
+				cursor.FormatTime(lastPost.CreatedAt),
+				lastPost.ID,
+				cursor.SortByCreatedAtDesc,
+			).Encode()
+		}
+		firstPost := posts[0]
+		prevCursor = cursor.NewCursor(
+			cursor.FormatTime(firstPost.CreatedAt),
+			firstPost.ID,
+			cursor.SortByCreatedAtDesc,
+		).Encode()
+	}
+
+	return cursor.NewCursorPageResult(posts, nextCursor, prevCursor, hasMore), nil
+}
+
+// GetHotPostsByCursor 游标分页获取热门帖子
+func (r *PostRepository) GetHotPostsByCursor(ctx context.Context, req *cursor.PageRequest) (*cursor.CursorPageResult[*model.Post], error) {
+	db := r.getDB(ctx).WithContext(ctx)
+
+	// 构建基础查询 - 热门帖子按热度分数排序
+	query := db.Model(&model.Post{}).Where("status = ?", model.PostStatusPublished).
+		Order("hot_score DESC, created_at DESC")
+
+	// 使用游标构建器
+	builder := cursor.NewBuilder(query, cursor.SortByCreatedAtDesc).
+		WithCursor(req.Cursor, req.Direction).
+		WithPageSize(req.PageSize)
+
+	if builder.Error() != nil {
+		// 无效游标，返回空列表
+		return cursor.NewCursorPageResult[*model.Post]([]*model.Post{}, "", "", false), nil
+	}
+
+	// 执行查询
+	var posts []*model.Post
+	query = builder.Build().Preload("User").Preload("Images")
+	if err := query.Find(&posts).Error; err != nil {
+		return nil, err
+	}
+
+	// 构建响应
+	pageSize := builder.GetPageSize()
+	hasMore := cursor.HasMore(len(posts), pageSize)
+	if hasMore {
+		posts = posts[:pageSize]
+	}
+
+	// 生成游标
+	var nextCursor, prevCursor string
+	if len(posts) > 0 {
+		if hasMore {
+			lastPost := posts[len(posts)-1]
+			nextCursor = cursor.NewCursor(
+				cursor.FormatTime(lastPost.CreatedAt),
+				lastPost.ID,
+				cursor.SortByCreatedAtDesc,
+			).Encode()
+		}
+		firstPost := posts[0]
+		prevCursor = cursor.NewCursor(
+			cursor.FormatTime(firstPost.CreatedAt),
+			firstPost.ID,
+			cursor.SortByCreatedAtDesc,
+		).Encode()
+	}
+
+	return cursor.NewCursorPageResult(posts, nextCursor, prevCursor, hasMore), nil
+}