feat: 后台评论管理 + 评论设置开关 + 技术债清理

- 后台评论管理页（待审核 Tab + 通过/拒绝），侧栏入口
- 站点设置加评论审核模式/评论邮件通知开关
- Material Icons 自托管（本地 woff2）+ ssr 图标修复
- /admin* 路由收紧为显式两条
- 删除死代码 routes/links.js
- 密码箱改 PIN 增加数据丢失警告确认

frontend/src/admin/main.jsx

@@ -18,6 +18,7 @@ import ThemeSettings from './pages/ThemeSettings.jsx';
 import Homepage from './pages/Homepage.jsx';
 import EmailSettings from './pages/EmailSettings.jsx';
 import BlogManage from './pages/BlogManage.jsx';
+import CommentManage from './pages/CommentManage.jsx';
 import ForumManage from './pages/ForumManage.jsx';
 import Users from './pages/Users.jsx';
 import Announcements from './pages/Announcements.jsx';
@@ -84,6 +85,7 @@ function AdminApp() {
             <Route path="/homepage" element={<Homepage />} />
             <Route path="/email" element={<EmailSettings />} />
             <Route path="/blog" element={<BlogManage />} />
+            <Route path="/comments" element={<CommentManage />} />
             <Route path="/forum" element={<ForumManage />} />
             <Route path="/users" element={<Users />} />
             <Route path="/announcements" element={<Announcements />} />