feat: 完成社区首页功能迭代，新增首页聚合与工作台组件

本次提交实现了完整的社区首页功能：
1. 新增首页聚合接口与服务，包含社区统计、热门帖、活跃用户与板块数据
2. 实现帖子推荐排序、SSR缓存与点赞态同步逻辑
3. 重构导航与布局系统，新增工作台侧边栏与移动端适配
4. 优化主题色与UI样式，统一设计系统风格
5. 修复登录注册页自动跳转与组件状态同步问题

frontend/components/home/CommunityPanels.tsx

@@ -0,0 +1,142 @@
+import Link from "next/link";
+import { BarChart3, Flame, Users, MessagesSquare, MessageCircle, Heart, Sparkles } from "lucide-react";
+import type { OverviewStats, PostListItem, ActiveUser } from "@/lib/api";
+import Avatar from "@/components/Avatar";
+
+/* ---------- 统计 2×2 ---------- */
+
+function StatsGrid({ stats }: { stats: OverviewStats }) {
+  const items = [
+    { icon: MessagesSquare, label: "讨论", value: stats.posts },
+    { icon: Users, label: "成员", value: stats.users },
+    { icon: MessageCircle, label: "评论", value: stats.comments },
+    { icon: Sparkles, label: "今日", value: stats.today_posts },
+  ];
+  return (
+    <section className="j13-module" aria-label="社区数据">
+      <p className="j13-module-title mb-3">
+        <BarChart3 size={15} style={{ color: "var(--accent)" }} /> 社区数据
+      </p>
+      <div className="grid grid-cols-2 gap-2">
+        {items.map(({ icon: Icon, label, value }) => (
+          <div key={label} className="j13-stat">
+            <span className="j13-stat-num">{value}</span>
+            <span className="j13-stat-lab">
+              <Icon size={12} /> {label}
+            </span>
+          </div>
+        ))}
+      </div>
+    </section>
+  );
+}
+
+/* ---------- 热门榜 ---------- */
+
+function HotRanking({ posts }: { posts: PostListItem[] }) {
+  return (
+    <section className="j13-module" aria-label="热门讨论">
+      <p className="j13-module-title mb-1.5">
+        <Flame size={15} style={{ color: "var(--clay)" }} /> 热门讨论
+      </p>
+      {posts.length === 0 ? (
+        <p className="meta px-1.5 py-3">还没有热门讨论</p>
+      ) : (
+        <ol className="j13-ranklist">
+          {posts.map((p, i) => (
+            <li key={p.id}>
+              <Link href={`/post/${p.id}`} className="j13-rank" title={p.title}>
+                <span className="j13-rank-no">{i + 1}</span>
+                <span className="min-w-0 flex-1">
+                  <span
+                    className="block text-[13.5px] font-semibold leading-snug line-clamp-2"
+                    style={{ color: "var(--ink)" }}
+                  >
+                    {p.title}
+                  </span>
+                  <span className="mt-1 flex items-center gap-2.5 meta text-[11.5px]">
+                    <span className="inline-flex items-center gap-1">
+                      <MessageCircle size={11.5} /> {p.comment_count}
+                    </span>
+                    <span className="inline-flex items-center gap-1">
+                      <Heart size={11.5} /> {p.like_count}
+                    </span>
+                    <span className="truncate">{p.board.name}</span>
+                  </span>
+                </span>
+              </Link>
+            </li>
+          ))}
+        </ol>
+      )}
+    </section>
+  );
+}
+
+/* ---------- 活跃用户 ---------- */
+
+function ActiveUsers({ users }: { users: ActiveUser[] }) {
+  return (
+    <section className="j13-module" aria-labelledby="active-users-title">
+      <p className="j13-module-title mb-3" id="active-users-title">
+        <Users size={15} style={{ color: "var(--accent)" }} /> 活跃成员
+      </p>
+      {users.length === 0 ? (
+        <p className="meta px-1.5 py-2">近 14 天还没有人互动</p>
+      ) : (
+        <ul className="space-y-1">
+          {users.map((u) => (
+            <li key={u.id}>
+              <Link href={`/u/${u.id}`} className="j13-raillink">
+                <Avatar name={u.nickname || u.username} src={u.avatar} size={28} />
+                <span className="flex-1 truncate text-[13.5px]">{u.nickname || u.username}</span>
+                <span className="meta text-[11.5px]">{u.activity_count} 次</span>
+              </Link>
+            </li>
+          ))}
+        </ul>
+      )}
+      <p className="meta mt-3 px-1 text-[11px]">按近 14 天发帖与评论计数</p>
+    </section>
+  );
+}
+
+/* ---------- 桌面 / 移动两种装配 ---------- */
+
+export function CommunityPanels({
+  stats,
+  hot,
+  activeUsers,
+}: {
+  stats: OverviewStats;
+  hot: PostListItem[];
+  activeUsers: ActiveUser[];
+}) {
+  return (
+    <aside className="hidden lg:block w-[280px] xl:w-[300px] shrink-0" aria-label="社区面板">
+      <div className="sticky top-24 space-y-4">
+        <StatsGrid stats={stats} />
+        <HotRanking posts={hot} />
+        <ActiveUsers users={activeUsers} />
+      </div>
+    </aside>
+  );
+}
+
+export function CommunityPanelsMobile({
+  stats,
+  hot,
+  activeUsers,
+}: {
+  stats: OverviewStats;
+  hot: PostListItem[];
+  activeUsers: ActiveUser[];
+}) {
+  return (
+    <div className="lg:hidden space-y-4" aria-label="社区面板">
+      <StatsGrid stats={stats} />
+      <HotRanking posts={hot} />
+      <ActiveUsers users={activeUsers} />
+    </div>
+  );
+}