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/App.tsx

@@ -11,7 +11,6 @@ import { OfficialRecommendationsPage } from "./pages/OfficialRecommendations";
 import { SearchPage } from "./pages/Search";
 import { PostRedirect } from "./pages/PostRedirect";
 import { ScrollToTop } from "./components/ScrollToTop";
-import { AboutPage } from "./pages/About";
 import Favorites from "./pages/Favorites";
 import { adminUiPrefix } from "./adminPaths";
 import { AdminRouteTree } from "./adminRouteTree";
@@ -46,7 +45,6 @@ export default function App() {
                       />
                       <Route path="/search" element={<SearchPage />} />
                       <Route path="/resource/:id" element={<PostRedirect />} />
-                      <Route path="/about" element={<AboutPage />} />
                       <Route path="/favorites" element={<Favorites />} />
                     </Route>