feat: 帖子收藏与用户关注

- 新增收藏功能：favorite 服务与 handler、FavoriteButton 组件
- 新增关注功能：follow 服务与 handler、FollowButton 组件
- 用户主页适配关注/粉丝与收藏展示
- flash 消息工具、广告与侧边栏组件微调

frontend/components/CommentSection.tsx

@@ -39,6 +39,8 @@ import MarkdownEditor from "@/components/MarkdownEditor";
 import ConfirmDialog from "@/components/ConfirmDialog";
 import DeleteCommentModal, { type DeleteCommentPayload } from "@/components/DeleteCommentModal";
 import EditHistoryModal from "@/components/EditHistoryModal";
+import { scrollFlashTo } from "@/lib/flash";
+import { fetchCommentLocation } from "@/lib/api";
 
 interface CommentSectionProps {
   postId: string;
@@ -288,6 +290,59 @@ export default function CommentSection({
     return () => window.removeEventListener("hashchange", focusComposer);
   }, [user, commentsOpen]);
 
+  // 深链定位：#comment-{id} → 滚动 + 主题色浅底高亮渐隐。
+  // 目标是折叠楼层里的子回复时先展开所属楼层；不在当前页时查楼层号换页后重试。
+  // 楼层号锚点（#楼）、「回复 @xx」、采纳答案卡等页内跳转经 hashchange 同样获得高亮。
+  const locatedRef = useRef<number | null>(null); // 已跨页尝试过的评论 ID，防循环
+  useEffect(() => {
+    if (!commentsOpen) return;
+    let cancelled = false;
+    const locate = async () => {
+      const m = window.location.hash.match(/^#comment-(\d+)$/);
+      if (!m) return;
+      const id = Number(m[1]);
+      const el = document.getElementById(`comment-${id}`);
+      if (el) {
+        scrollFlashTo(el);
+        return;
+      }
+      // 不在 DOM：先看是否在本页数据里（折叠的子回复）→ 展开所属楼层后定位
+      const node = findComment(comments, id);
+      if (node) {
+        const rootId = node.root_id ?? node.parent_id ?? node.id;
+        setExpandedFloors((prev) => {
+          if (prev.has(rootId)) return prev;
+          const next = new Set(prev);
+          next.add(rootId);
+          return next;
+        });
+        window.setTimeout(() => {
+          if (!cancelled) scrollFlashTo(document.getElementById(`comment-${id}`));
+        }, 160);
+        return;
+      }
+      // 不在本页：查楼层号 → 换页（comments 变化后本 effect 再次运行并定位）
+      if (locatedRef.current === id) return; // 已尝试仍找不到（如被拒/未公开），放弃
+      locatedRef.current = id;
+      try {
+        const floor = await fetchCommentLocation(postId, id);
+        if (cancelled || floor <= 0) return;
+        const destPage = Math.max(1, Math.ceil(floor / size));
+        if (destPage === page) return; // 同页却无节点（异常数据），放弃
+        router.replace(`/post/${postId}?page=${destPage}#comment-${id}`, { scroll: false });
+      } catch {
+        /* 定位失败静默：停留在当前页 */
+      }
+    };
+    locate();
+    window.addEventListener("hashchange", locate);
+    return () => {
+      cancelled = true;
+      window.removeEventListener("hashchange", locate);
+    };
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [comments, commentsOpen, page, postId, size]);
+
   const submitFloor = async () => {
     if (!commentsOpen || !content.trim() || submitLock.current || floorUploading) return;
     submitLock.current = true;