xhs_get_comments 增加 sort + max_count 控制，评论随详情一起返回

- Comment 新增 subCommentCount，新增 CommentsResult 接口
- GetFeedCommentsSchema 替换 load_all 为 sort (default/newest/most_liked) + max_count (1-100)
- getFeedDetail 不再清空评论，从 Vue store 异步提取首屏评论（轮询 firstRequestFinish）
- getFeedComments 重写：支持排序切换、按 maxCount 加载、返回 hasMore/totalCount
- 前端详情加载后直接显示评论，无需单独请求；底部显示"加载更多评论"按钮
- CommentTree 显示"还有 X 条回复"提示
- 修复 formatTime 对空字符串和无效日期的处理

src/platforms/xiaohongshu/selectors.ts

@@ -85,13 +85,13 @@ export const XHS_SELECTORS = {
     /** Comment list container. */
     commentListContainer: '.comments-container .list-container',
     /** Individual top-level comment items. */
-    commentItem: '.comments-container .list-container .list-item',
+    commentItem: '.comments-container .list-container > .parent-comment > .comment-item',
     /** Parent comment content text. */
     commentContent: '.content',
     /** Comment author name. */
     commentAuthor: '.author .name',
     /** Comment author avatar. */
-    commentAvatar: '.author .avatar img',
+    commentAvatar: '.avatar img.avatar-item',
     /** Comment like count. */
     commentLikeCount: '.like .count',
     /** Comment publish time. */
@@ -104,6 +104,14 @@ export const XHS_SELECTORS = {
     showMoreComments: '.comments-container .show-more',
     /** "Load more replies" button within a comment thread. */
     loadMoreReplies: '.sub-comment-list .show-more',
+    /** Comment sort tab — default (热度). */
+    commentSortDefault: '.comments-container .tab:first-child, .comments-container .sort-tab:first-child',
+    /** Comment sort tab — newest (最新). */
+    commentSortNewest: '.comments-container .tab:nth-child(2), .comments-container .sort-tab:nth-child(2)',
+    /** Comment sort tab — most liked (最热). */
+    commentSortHottest: '.comments-container .tab:nth-child(3), .comments-container .sort-tab:nth-child(3)',
+    /** Sub-comment count text element (e.g. "展开 X 条回复"). */
+    subCommentCountText: '.sub-comment-list .show-more, .reply-container .show-more',
   },
 
   userProfile: {