feat: 调整 Feed 排序为新评论/新帖子/推荐帖

默认按新评论；推荐排序优先 featured，并将用户可见「精华」文案改为「推荐」。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/pages/admin/AdminDashboardPage.tsx

@@ -245,7 +245,7 @@ export default function AdminDashboardPage() {
                   ) : '—'}
                 </td>
                 <td className="space-x-1">
-                  {p.featured ? <Badge variant="orange">精华</Badge> : null}
+                  {p.featured ? <Badge variant="orange">推荐</Badge> : null}
                   {p.pinned ? <Badge variant="green">全局置顶</Badge> : null}
                   {p.board_pinned ? <Badge variant="green">板块置顶</Badge> : null}
                   {!p.featured && !p.pinned && !p.board_pinned ? '—' : null}