xhs_get_comments → xhs_get_sub_comments：针对单条评论加载子评论

getFeedDetail 已返回首屏一级评论（含 1-2 条子评论预览），不再需要独立的
评论加载工具。新增 xhs_get_sub_comments 针对指定一级评论加载完整子评论，
支持 max_count 参数（默认 20）控制加载量，避免超时和上下文溢出。

后端：
- schemas: GetFeedCommentsSchema → GetSubCommentsSchema (feed_id, xsec_token, comment_id, max_count)
- types: 删除 CommentsResult
- feed-detail: 删除 getFeedComments/scrapeComments/CommentSort/parseCommentElement，
  新增 getSubComments（导航→store就绪→定位评论→点击展开→读store）
- selectors: 删除 commentSort* 选择器
- index/routes: 注册新工具和路由，超时改用 feed_detail（60s）

前端：
- types/endpoints: 删除 CommentsResult，新增 getSubComments API
- FeedDetail: 删除独立评论加载逻辑，评论随详情显示，新增 handleLoadSubComments
- CommentTree: "还有 X 条回复" 改为可点击按钮，带加载状态

web/src/components/feed/FeedDetail.tsx

@@ -1,6 +1,6 @@
 import { useState, useEffect } from 'react';
 import type { FeedDetail as FeedDetailType, Comment } from '@/api/types';
-import { getFeedDetail, getFeedComments, toggleLike, toggleFavorite, postComment, replyComment } from '@/api/endpoints';
+import { getFeedDetail, getSubComments, toggleLike, toggleFavorite, postComment, replyComment } from '@/api/endpoints';
 import { Badge } from '@/components/ui/Badge';
 import { Spinner } from '@/components/ui/Spinner';
 import { Button } from '@/components/ui/Button';
@@ -24,10 +24,7 @@ export function FeedDetail({ feedId, xsecToken, onClose, onUserClick }: Props) {
   const [currentImage, setCurrentImage] = useState(0);
 
   const [comments, setComments] = useState<Comment[]>([]);
-  const [commentsLoading, setCommentsLoading] = useState(false);
-  const [commentsHasMore, setCommentsHasMore] = useState(false);
-  const [commentsTotalCount, setCommentsTotalCount] = useState(0);
-  const [commentsMaxCount, setCommentsMaxCount] = useState(20);
+  const [subCommentsLoading, setSubCommentsLoading] = useState<string | null>(null);
 
   const [liked, setLiked] = useState(false);
   const [favorited, setFavorited] = useState(false);
@@ -49,8 +46,6 @@ export function FeedDetail({ feedId, xsecToken, onClose, onUserClick }: Props) {
           // Use comments from __INITIAL_STATE__ (first page, ~10-20).
           if (res.data.comments.length > 0) {
             setComments(res.data.comments);
-            setCommentsTotalCount(res.data.commentCount);
-            setCommentsHasMore(res.data.commentCount > res.data.comments.length);
           }
         } else {
           setError(res.error?.message || 'Failed to load detail');
@@ -61,28 +56,26 @@ export function FeedDetail({ feedId, xsecToken, onClose, onUserClick }: Props) {
 
   }, [feedId, xsecToken]);
 
-  const handleLoadComments = async (maxCount = commentsMaxCount) => {
-    setCommentsLoading(true);
+  const handleLoadSubComments = async (commentId: string) => {
+    setSubCommentsLoading(commentId);
     try {
-      const res = await getFeedComments(feedId, xsecToken, 'default', maxCount);
+      const res = await getSubComments(feedId, xsecToken, commentId);
       if (res.success && res.data) {
-        setComments(res.data.comments);
-        setCommentsHasMore(res.data.hasMore);
-        setCommentsTotalCount(res.data.totalCount);
+        setComments((prev) =>
+          prev.map((c) =>
+            c.id === commentId
+              ? { ...c, subComments: res.data!, subCommentCount: res.data!.length }
+              : c,
+          ),
+        );
       }
     } catch {
-      toast('error', '加载评论失败');
+      toast('error', '加载子评论失败');
     } finally {
-      setCommentsLoading(false);
+      setSubCommentsLoading(null);
     }
   };
 
-  const handleLoadMore = () => {
-    const nextCount = commentsMaxCount * 2;
-    setCommentsMaxCount(nextCount);
-    void handleLoadComments(nextCount);
-  };
-
   const handleToggleLike = async () => {
     setActionLoading('like');
     try {
@@ -323,25 +316,10 @@ export function FeedDetail({ feedId, xsecToken, onClose, onUserClick }: Props) {
             </div>
 
             {/* Comments */}
-            {comments.length === 0 && !commentsLoading && (
-              <Button
-                size="sm"
-                variant="secondary"
-                onClick={() => void handleLoadComments()}
-              >
-                加载评论
-              </Button>
-            )}
-            {commentsLoading && (
-              <div className="flex items-center gap-2 py-4 text-dark-muted text-sm">
-                <Spinner size="sm" />
-                <span>加载评论中...</span>
-              </div>
-            )}
             {comments.length > 0 && (
               <div>
                 <h3 className="text-sm font-semibold text-dark-muted uppercase tracking-wider mb-3">
-                  评论 ({commentsTotalCount > 0 ? commentsTotalCount : comments.length})
+                  评论 ({detail.commentCount > 0 ? detail.commentCount : comments.length})
                 </h3>
                 <CommentTree
                   comments={comments}
@@ -349,17 +327,9 @@ export function FeedDetail({ feedId, xsecToken, onClose, onUserClick }: Props) {
                     setReplyTarget({ commentId, userId, nickname });
                     setReplyText('');
                   }}
+                  onLoadSubComments={(commentId) => void handleLoadSubComments(commentId)}
+                  subCommentsLoadingId={subCommentsLoading}
                 />
-                {commentsHasMore && !commentsLoading && (
-                  <Button
-                    size="sm"
-                    variant="secondary"
-                    onClick={handleLoadMore}
-                    className="mt-3 w-full"
-                  >
-                    加载更多评论
-                  </Button>
-                )}
               </div>
             )}
           </div>