feat(admin): 合并内容审核到内容管理，并固定后台侧栏

待审与内容库同一页处理；筛选切换去掉加载占位，避免页面闪动。

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

frontend/app/admin/page.tsx

@@ -56,14 +56,18 @@ function PanelHead({ title, extra }: { title: string; extra?: string }) {
   );
 }
 
-/** 待办：待审帖子 / 评论，整块进入审核页 */
+/** 待办：待审帖子 / 评论，进入内容管理的待审筛选 */
 function PendingWorkPanel({ counts }: { counts: PendingCounts }) {
   const total = counts.posts + counts.comments;
   const idle = total === 0;
 
   return (
     <Link
-      href="/admin/moderation"
+      href={
+        counts.posts > 0 || counts.comments === 0
+          ? "/admin/content?status=pending"
+          : "/admin/content?status=pending&kind=comments"
+      }
       className="panel hover-lift relative block p-4 sm:p-5 mb-4 group"
     >
       <div className="flex items-start gap-3.5">
@@ -80,7 +84,7 @@ function PendingWorkPanel({ counts }: { counts: PendingCounts }) {
         <div className="min-w-0 flex-1">
           <div className="flex items-center gap-2 flex-wrap">
             <p className="text-[15px] font-semibold" style={{ color: "var(--ink)" }}>
-              内容审核
+              待审内容
             </p>
             {idle ? (
               <span