feat: 移除「关于本站」按钮与功能

- PublicLayout: 删除桌面导航/下拉菜单/页脚三处入口及空页脚,移除 about 导航类型与判断
- App: 移除 /about 路由及 AboutPage 引入
- 删除 pages/About 页面
- DocumentMeta: 移除 /about 的 meta 处理与 about 描述文案(中/英)
- i18n: 移除 aboutTitle / aboutIntro / footerAbout(中/英)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/pages/About/index.tsx

@@ -1,18 +0,0 @@
-import { useI18n } from "../../i18n";
-import { Reveal } from "../../motion";
-
-export function AboutPage() {
-  const { t } = useI18n();
-  return (
-    <div className="mx-auto max-w-2xl space-y-6">
-      <Reveal>
-        <h1 className="text-2xl font-bold">{t("aboutTitle")}</h1>
-      </Reveal>
-      <Reveal delay={0.08}>
-        <p className="text-neutral-300 leading-relaxed whitespace-pre-line">
-          {t("aboutIntro")}
-        </p>
-      </Reveal>
-    </div>
-  );
-}