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/NotificationBell.tsx

@@ -3,7 +3,7 @@
 import { useState, useEffect, useRef } from "react";
 import { useRouter } from "next/navigation";
 import Link from "next/link";
-import { Bell, CheckCheck, Heart, MessageCircle, CheckCircle2, XCircle, AtSign, ClipboardList, Award, AlertTriangle } from "lucide-react";
+import { Bell, CheckCheck, Heart, MessageCircle, CheckCircle2, XCircle, AtSign, ClipboardList, Award, AlertTriangle, UserPlus } from "lucide-react";
 import {
   apiFetchNotifications,
   apiUnreadCount,
@@ -99,13 +99,18 @@ export default function NotificationBell({ initialUnread = 0 }: { initialUnread?
       );
     }
     setOpen(false);
-    // @提及通知跳到群聊房间；徽章通知无关联帖子（仅标已读）；其余跳到帖子/评论
+    // @提及通知跳到群聊房间；徽章通知无关联帖子（仅标已读）；关注通知跳到关注者主页；其余跳到帖子/评论
     if (n.type === "mention" && n.room_id) {
       router.push(`/chat/${n.room_id}`);
     } else if (n.type === "pending_review") {
       router.push(n.post_id ? `/post/${n.post_id}` : "/admin/content?status=pending");
     } else if (n.type === "badge") {
       return;
+    } else if (n.type === "follow") {
+      router.push(`/u/${n.actor_id}`);
+    } else if (n.comment_id > 0) {
+      // 评论/回复/点赞等：直达评论所在楼层（跨页由帖子页深链定位换页）
+      router.push(`/post/${n.post_id}#comment-${n.comment_id}`);
     } else {
       router.push(`/post/${n.post_id}`);
     }
@@ -138,6 +143,7 @@ export default function NotificationBell({ initialUnread = 0 }: { initialUnread?
     if (n.type === "deleted") return "删除了你的帖子";
     if (n.type === "badge") return "向你颁布了徽章";
     if (n.type === "necro_reply") return "旧帖回复提醒";
+    if (n.type === "follow") return "关注了你";
     return "点赞了你的帖子";
   };
 
@@ -161,6 +167,8 @@ export default function NotificationBell({ initialUnread = 0 }: { initialUnread?
       return { color: "var(--accent)", bg: "var(--accent-soft)", node: <ClipboardList size={15} /> };
     if (n.type === "badge")
       return { color: "var(--gold)", bg: "var(--gold-soft)", node: <Award size={15} /> };
+    if (n.type === "follow")
+      return { color: "var(--accent)", bg: "var(--accent-soft)", node: <UserPlus size={15} /> };
     return { color: "var(--accent)", bg: "var(--accent-soft)", node: <MessageCircle size={15} /> };
   };