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/app/page.tsx

@@ -14,7 +14,6 @@ import PostRow from "@/components/PostRow";
 import FeedTabs, { type FeedSort } from "@/components/home/FeedTabs";
 import { WorkspaceNav, WorkspaceNavMobile } from "@/components/home/WorkspaceNav";
 import { CommunityPanels, CommunityPanelsMobile } from "@/components/home/CommunityPanels";
-import HomeHero from "@/components/home/HomeHero";
 
 export const metadata: Metadata = {
   title: "姜十三论坛 · 技术讨论社区",
@@ -26,7 +25,10 @@ interface HomePageProps {
 }
 
 function normalizeSort(v?: string): FeedSort {
-  return v === "hot" || v === "recommended" ? v : "latest";
+  if (v === "new" || v === "recommended") return v;
+  // 兼容旧的 ?sort=hot 链接：落到最接近的推荐帖
+  if (v === "hot") return "recommended";
+  return "latest";
 }
 
 // 空结果面板（无帖 / 无搜索结果）
@@ -125,25 +127,14 @@ export default async function HomePage({ searchParams }: HomePageProps) {
     );
   }
 
-  // 置顶帖直接按后端 pinned DESC 顺序并入统一信息流，同样的行布局
+  // 置顶帖直接按后端 pinned DESC 顺序并入统一信息流；标题仅供屏幕阅读器
   const heading = activeBoard
     ? activeBoard.name
-    : sort === "hot"
-      ? "热门讨论"
+    : sort === "new"
+      ? "最新发布"
       : sort === "recommended"
-        ? "精华内容"
+        ? "推荐帖"
         : "最新讨论";
-  const headingHint = activeBoard
-    ? sort === "hot"
-      ? "该板块按点赞与评论热度排序"
-      : sort === "recommended"
-        ? "该板块管理员精选的优质内容"
-        : "该板块新发帖与新评论都会浮到顶部"
-    : sort === "hot"
-      ? "按点赞与评论热度排序"
-      : sort === "recommended"
-        ? "管理员精选的优质内容"
-        : "新发帖与新评论都会浮到顶部";
 
   const pageQuery: Record<string, string> = {};
   if (boardId > 0) pageQuery.board = String(boardId);
@@ -151,31 +142,22 @@ export default async function HomePage({ searchParams }: HomePageProps) {
 
   return (
     <div>
-      <HomeHero user={user} stats={overview?.stats ?? null} />
-
       <WorkspaceNavMobile boards={boards} user={user} />
 
       <div className="flex items-start gap-6 xl:gap-7 mt-5 lg:mt-0">
         <WorkspaceNav boards={boards} user={user} />
 
-        {/* 中栏：帖子流（左栏切板块只替换这一列） */}
+        {/* 中栏：tab 栏与帖子流为同一个整体卡片（左栏切板块只替换这一列） */}
         <div className="flex-1 min-w-0">
-          <div className="flex items-end justify-between gap-3 flex-wrap mb-4">
-            <div className="min-w-0">
-              <h1
-                className="text-[23px] sm:text-[27px] font-extrabold tracking-tight"
-                style={{ color: "var(--ink)" }}
-              >
-                {heading}
-              </h1>
-              <p className="meta mt-1.5">
-                共 {postsData.total} 篇 · {headingHint}
-              </p>
-            </div>
-            <FeedTabs current={sort} boardId={boardId} />
-          </div>
+          <h1 className="sr-only">{heading}</h1>
 
           <div className="panel overflow-hidden">
+            <div className="flex items-center justify-between gap-2 px-3 sm:px-4 pt-3 pb-2.5">
+              <FeedTabs current={sort} boardId={boardId} />
+              <span className="meta shrink-0 text-[12px] tabular-nums">
+                共 {postsData.total} 篇
+              </span>
+            </div>
             {postsData.posts.length > 0 ? (
               postsData.posts.map((post, i) => (
                 <PostRow
@@ -204,14 +186,27 @@ export default async function HomePage({ searchParams }: HomePageProps) {
 
         {/* 右栏：社区面板 */}
         {overview && (
-          <CommunityPanels hot={overview.hot} activeUsers={overview.active_users} />
+          <CommunityPanels
+            stats={overview.stats}
+            hot={overview.hot}
+            activeUsers={overview.active_users}
+            latestComments={overview.latest_comments}
+            newUsers={overview.new_users}
+            checkin={overview.checkin ?? undefined}
+          />
         )}
       </div>
 
       {/* 窄屏：面板下沉到帖子流之后 */}
       {overview && (
         <div className="mt-6">
-          <CommunityPanelsMobile hot={overview.hot} activeUsers={overview.active_users} />
+          <CommunityPanelsMobile
+            hot={overview.hot}
+            activeUsers={overview.active_users}
+            latestComments={overview.latest_comments}
+            newUsers={overview.new_users}
+            checkin={overview.checkin ?? undefined}
+          />
         </div>
       )}
     </div>