feat: 添加每日签到功能，新增帖子排序与社区面板优化

本次提交完成了多个核心功能迭代：
1.  新增用户每日签到系统，包含签到状态查询、连续天数统计、积分累计逻辑
2.  新增"新帖子"排序选项，替换原有的latest排序为新评论排序
3.  重构首页信息流布局，优化移动端与桌面端展示样式
4.  新增最新评论、最新注册用户模块，完善社区面板数据展示
5.  新增静态友情链接配置模块
6.  提取通用时间格式化工具函数，统一全站相对时间展示
7.  补充数据库签到模型与后端API接口，完善前后端交互链路

frontend/components/home/CommunityPanels.tsx

@@ -1,7 +1,106 @@
 import Link from "next/link";
-import { Flame, Users, MessageCircle, Heart } from "lucide-react";
-import type { PostListItem, ActiveUser } from "@/lib/api";
+import {
+  Flame,
+  Users,
+  MessageCircle,
+  Heart,
+  MessageSquareText,
+  UserPlus,
+  Link2,
+} from "lucide-react";
+import type {
+  PostListItem,
+  ActiveUser,
+  OverviewStats,
+  LatestComment,
+  NewUser,
+  CheckinStatus,
+} from "@/lib/api";
 import Avatar from "@/components/Avatar";
+import CheckinCard from "./CheckinCard";
+import { FRIEND_LINKS } from "@/lib/friendLinks";
+import { formatRelative } from "@/lib/format";
+
+/* ---------- 品牌卡 ---------- */
+
+function BrandCard({ stats }: { stats: OverviewStats }) {
+  const items: { num: number; label: string }[] = [
+    { num: stats.posts, label: "帖子" },
+    { num: stats.comments, label: "回复" },
+    { num: stats.users, label: "用户" },
+  ];
+  return (
+    <section className="j13-module text-center" aria-label="姜十三论坛">
+      <p className="text-[16.5px] font-extrabold tracking-wide" style={{ color: "var(--accent)" }}>
+        姜十三论坛
+      </p>
+      <p className="meta mt-1 text-[12px]">分享技术、讨论问题、交流心得</p>
+      <div
+        className="mt-3.5 pt-3.5 grid grid-cols-3"
+        style={{ borderTop: "1px solid var(--line)" }}
+      >
+        {items.map((it) => (
+          <div key={it.label}>
+            <p
+              className="text-[19px] font-extrabold tabular-nums leading-none"
+              style={{ color: "var(--accent)" }}
+            >
+              {it.num}
+            </p>
+            <p className="meta mt-1.5 text-[11.5px]">{it.label}</p>
+          </div>
+        ))}
+      </div>
+    </section>
+  );
+}
+
+/* ---------- 最新评论 ---------- */
+
+function LatestComments({ comments }: { comments: LatestComment[] }) {
+  if (comments.length === 0) return null;
+  return (
+    <section className="j13-module" aria-label="最新评论">
+      <p className="j13-module-title mb-1">
+        <MessageSquareText size={15} style={{ color: "var(--accent)" }} /> 最新评论
+      </p>
+      <ul>
+        {comments.map((c) => {
+          const name = c.user.nickname || c.user.username;
+          return (
+            <li key={c.id}>
+              <Link href={`/post/${c.post.id}`} className="j13-raillink items-start">
+                <Avatar name={name} src={c.user.avatar} size={28} className="mt-px" />
+                <span className="min-w-0 flex-1">
+                  <span className="flex items-baseline gap-1.5">
+                    <span
+                      className="shrink-0 max-w-[84px] truncate text-[12.5px] font-semibold"
+                      style={{ color: "var(--ink-2)" }}
+                    >
+                      {name}
+                    </span>
+                    <span
+                      className="min-w-0 flex-1 truncate text-[13px]"
+                      style={{ color: "var(--ink-2)" }}
+                    >
+                      {c.content}
+                    </span>
+                  </span>
+                  <span className="meta mt-0.5 block truncate text-[11.5px]">
+                    {c.post.title}
+                  </span>
+                </span>
+                <span className="meta mt-px shrink-0 text-[11px]">
+                  {formatRelative(c.created_at)}
+                </span>
+              </Link>
+            </li>
+          );
+        })}
+      </ul>
+    </section>
+  );
+}
 
 /* ---------- 热门榜 ---------- */
 
@@ -45,6 +144,41 @@ function HotRanking({ posts }: { posts: PostListItem[] }) {
   );
 }
 
+/* ---------- 最新注册 ---------- */
+
+function NewUsers({ users }: { users: NewUser[] }) {
+  if (users.length === 0) return null;
+  return (
+    <section className="j13-module" aria-label="最新注册">
+      <p className="j13-module-title mb-3">
+        <UserPlus size={15} style={{ color: "var(--accent)" }} /> 最新注册
+      </p>
+      <ul className="grid grid-cols-4 gap-y-3">
+        {users.map((u) => {
+          const name = u.nickname || u.username;
+          return (
+            <li key={u.id}>
+              <Link
+                href={`/u/${u.id}`}
+                className="flex flex-col items-center gap-1.5 rounded-lg px-1 py-1 transition-colors hover:bg-[var(--panel-2)]"
+              >
+                <Avatar name={name} src={u.avatar} size={38} />
+                <span
+                  className="w-full truncate text-center text-[11px]"
+                  style={{ color: "var(--ink-2)" }}
+                  title={name}
+                >
+                  {name}
+                </span>
+              </Link>
+            </li>
+          );
+        })}
+      </ul>
+    </section>
+  );
+}
+
 /* ---------- 活跃用户 ---------- */
 
 function ActiveUsers({ users }: { users: ActiveUser[] }) {
@@ -73,20 +207,72 @@ function ActiveUsers({ users }: { users: ActiveUser[] }) {
   );
 }
 
+/* ---------- 友情链接 ---------- */
+
+function FriendLinks() {
+  return (
+    <section className="j13-module" aria-label="友情链接">
+      <p className="j13-module-title mb-3">
+        <Link2 size={15} style={{ color: "var(--accent)" }} /> 友情链接
+        <Link
+          href="/compose"
+          className="meta ml-auto text-[12px] font-normal transition-colors hover:text-[var(--accent)]"
+        >
+          申请
+        </Link>
+      </p>
+      <div className="flex flex-wrap gap-2">
+        {FRIEND_LINKS.map((l) =>
+          l.href.startsWith("http") ? (
+            <a
+              key={l.name}
+              href={l.href}
+              target="_blank"
+              rel="noopener noreferrer"
+              className="j13-chip"
+            >
+              {l.name}
+            </a>
+          ) : (
+            <span key={l.name} className="j13-chip" title="友链待配置">
+              {l.name}
+            </span>
+          )
+        )}
+      </div>
+    </section>
+  );
+}
+
 /* ---------- 桌面 / 移动两种装配 ---------- */
 
-export function CommunityPanels({
-  hot,
-  activeUsers,
-}: {
+type PanelsProps = {
+  stats: OverviewStats;
   hot: PostListItem[];
   activeUsers: ActiveUser[];
-}) {
+  latestComments: LatestComment[];
+  newUsers: NewUser[];
+  checkin?: CheckinStatus | null;
+};
+
+export function CommunityPanels({
+  stats,
+  hot,
+  activeUsers,
+  latestComments,
+  newUsers,
+  checkin,
+}: PanelsProps) {
   return (
-    <aside className="hidden lg:block w-[280px] xl:w-[300px] shrink-0" aria-label="社区面板">
+    <aside className="hidden w-[280px] shrink-0 lg:block xl:w-[300px]" aria-label="社区面板">
       <div className="sticky top-24 space-y-4">
+        <BrandCard stats={stats} />
+        <CheckinCard initial={checkin} />
+        <LatestComments comments={latestComments} />
         <HotRanking posts={hot} />
+        <NewUsers users={newUsers} />
         <ActiveUsers users={activeUsers} />
+        <FriendLinks />
       </div>
     </aside>
   );
@@ -95,14 +281,18 @@ export function CommunityPanels({
 export function CommunityPanelsMobile({
   hot,
   activeUsers,
-}: {
-  hot: PostListItem[];
-  activeUsers: ActiveUser[];
-}) {
+  latestComments,
+  newUsers,
+  checkin,
+}: Omit<PanelsProps, "stats">) {
   return (
-    <div className="lg:hidden space-y-4" aria-label="社区面板">
+    <div className="space-y-4 lg:hidden" aria-label="社区面板">
+      <CheckinCard initial={checkin} />
+      <LatestComments comments={latestComments} />
       <HotRanking posts={hot} />
+      <NewUsers users={newUsers} />
       <ActiveUsers users={activeUsers} />
+      <FriendLinks />
     </div>
   );
 }