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/FeedTabs.tsx

@@ -3,15 +3,11 @@
 import Link from "next/link";
 import { useRouter } from "next/navigation";
 import { useRef } from "react";
+import { MessageSquareText, Clock, Sparkles } from "lucide-react";
 
-export type FeedSort = "latest" | "hot" | "recommended";
+export type FeedSort = "latest" | "new" | "recommended";
 
-const TAB_KEYS: FeedSort[] = ["latest", "hot", "recommended"];
-const TAB_LABELS: Record<FeedSort, string> = {
-  latest: "最新",
-  hot: "热门",
-  recommended: "精华",
-};
+const TAB_KEYS: FeedSort[] = ["latest", "new", "recommended"];
 
 // 在指定板块内切换排序时保留 ?board=
 function tabHref(key: FeedSort, boardId: number) {
@@ -36,22 +32,27 @@ export default function FeedTabs({ current, boardId = 0 }: { current: FeedSort;
   };
 
   return (
-    <div className="j13-seg" role="tablist" aria-label="帖子排序">
-      {TAB_KEYS.map((key, i) => (
-        <Link
-          key={key}
-          ref={(el) => {
-            tabRefs.current[i] = el;
-          }}
-          href={tabHref(key, boardId)}
-          role="tab"
-          aria-selected={current === key}
-          tabIndex={current === key ? 0 : -1}
-          onKeyDown={(e) => handleKeyDown(e, i)}
-        >
-          {TAB_LABELS[key]}
-        </Link>
-      ))}
+    <div className="flex items-center gap-1.5 sm:gap-2" role="tablist" aria-label="帖子排序">
+      {TAB_KEYS.map((key, i) => {
+        const Icon = key === "latest" ? MessageSquareText : key === "new" ? Clock : Sparkles;
+        return (
+          <Link
+            key={key}
+            ref={(el) => {
+              tabRefs.current[i] = el;
+            }}
+            href={tabHref(key, boardId)}
+            role="tab"
+            className="j13-tab inline-flex items-center gap-1"
+            aria-selected={current === key}
+            tabIndex={current === key ? 0 : -1}
+            onKeyDown={(e) => handleKeyDown(e, i)}
+          >
+            <Icon size={13} className="opacity-80" />
+            {key === "latest" ? "新评论" : key === "new" ? "新帖子" : "推荐帖"}
+          </Link>
+        );
+      })}
     </div>
   );
 }