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/app/notifications/NotificationsClient.tsx

@@ -3,7 +3,7 @@
 import { useState } from "react";
 import { useRouter } from "next/navigation";
 import Link from "next/link";
-import { Heart, MessageCircle, CheckCheck, Bell, CheckCircle2, XCircle, AtSign, ClipboardList, Award, AlertTriangle } from "lucide-react";
+import { Heart, MessageCircle, CheckCheck, Bell, CheckCircle2, XCircle, AtSign, ClipboardList, Award, AlertTriangle, UserPlus } from "lucide-react";
 import { apiMarkRead, apiMarkAllRead, type NotificationsResponse, type NotificationItem } from "@/lib/api";
 
 /**
@@ -20,13 +20,18 @@ export default function NotificationsClient({ initialData }: { initialData: Noti
         list.map((item) => (item.id === n.id ? { ...item, is_read: true } : item))
       );
     }
-    // @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}`);
     }
@@ -92,7 +97,9 @@ export default function NotificationsClient({ initialData }: { initialData: Noti
                         ? <ClipboardList size={16} />
                         : n.type === "badge"
                           ? <Award size={16} />
-                          : <MessageCircle size={16} />;
+                          : n.type === "follow"
+                            ? <UserPlus size={16} />
+                            : <MessageCircle size={16} />;
             const iconColor = n.type === "approved"
               ? "var(--ok)"
               : n.type === "rejected" || n.type === "deleted" || n.type === "necro_reply"
@@ -162,7 +169,9 @@ export default function NotificationsClient({ initialData }: { initialData: Noti
                                 : n.type === "deleted"
                                   ? "删除了你的帖子"
                                   : n.type === "badge"
-                                    ? "向你颁布了徽章"
+                                  ? "向你颁布了徽章"
+                                  : n.type === "follow"
+                                    ? "关注了你"
                                     : "点赞了你的帖子"}
                       </span>
                     </>