feat: RSS 三源（博客/论坛全站/版块级）+ 后台 RSS 管理页 + 前台订阅按钮 + SSR head 注入

frontend/src/admin/main.jsx

@@ -21,6 +21,7 @@ import BlogManage from './pages/BlogManage.jsx';
 import CommentManage from './pages/CommentManage.jsx';
 import ForumManage from './pages/ForumManage.jsx';
 import PostManage from './pages/PostManage.jsx';
+import RssManage from './pages/RssManage.jsx';
 import Users from './pages/Users.jsx';
 import Announcements from './pages/Announcements.jsx';
 import Links from './pages/Links.jsx';
@@ -106,6 +107,7 @@ function AdminApp() {
             <Route path="/comments" element={<CommentManage />} />
             <Route path="/forum" element={<ForumManage />} />
             <Route path="/posts" element={<PostManage />} />
+            <Route path="/rss" element={<RssManage />} />
             <Route path="/users" element={<Users />} />
             <Route path="/announcements" element={<Announcements />} />
             <Route path="/links" element={<Links />} />