feat(home): add homepage hero banner and migrate community stats

- 新增首页欢迎横幅组件，包含时段问候、用户问候语、发帖引导按钮和社区统计数据
- 从CommunityPanels中移除stats相关逻辑，将社区统计迁移到新的HomeHero组件中
- 优化全局样式，添加横幅相关的CSS动画和样式类

frontend/components/home/CommunityPanels.tsx

@@ -1,36 +1,8 @@
 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 { Flame, Users, MessageCircle, Heart } from "lucide-react";
+import type { 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[] }) {
@@ -77,8 +49,8 @@ function HotRanking({ posts }: { posts: PostListItem[] }) {
 
 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">
+    <section className="j13-module" aria-label="活跃成员">
+      <p className="j13-module-title mb-3">
         <Users size={15} style={{ color: "var(--accent)" }} /> 活跃成员
       </p>
       {users.length === 0 ? (
@@ -104,18 +76,15 @@ function ActiveUsers({ users }: { users: ActiveUser[] }) {
 /* ---------- 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>
@@ -124,17 +93,14 @@ export function CommunityPanels({
 }
 
 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>