Advertise the Agent Markdown entrypoint from feed pages

src/components/Feed.tsx

@@ -31,7 +31,7 @@ export function Feed({initial,section='',tagPath=''}:{initial:FeedData;section?:
  useEffect(()=>{generation.current++;setPosts(initial.posts);setCursor(initial.nextCursor);setError('');setBusy(false);},[initial,router.query.q]);
  const current=sections.find(s=>s.path===section);const target=initial.tags.find(t=>t.path===tagPath);const children=initial.tags.filter(t=>target?t.parent_id===target.id:!t.parent_id);
  async function load(){const gen=generation.current;setBusy(true);setError('');try{const q=new URLSearchParams({section,path:tagPath,cursor:cursor||'',q:String(router.query.q||'')});const res=await fetch('/api/feed?'+q);const d=await res.json();if(!res.ok)throw new Error(d.error);if(gen===generation.current){setPosts(old=>[...old,...d.posts.filter((p:Post)=>!old.some(a=>a.id===p.id))]);setCursor(d.nextCursor);}}catch{if(gen===generation.current)setError('加载没有完成，点击重试。');}finally{if(gen===generation.current)setBusy(false);}}
- return <Shell><Head><title>{target?.name||current?.name||'灵感首页'} · PROMPT</title><meta name="description" content="自己的图文、视频与声音创作空间"/></Head>
+ return <Shell><Head><title>{target?.name||current?.name||'灵感首页'} · PROMPT</title><meta name="description" content="自己的图文、视频与声音创作空间"/><link rel="alternate" type="text/markdown" href="/agent/index.md" title="Agent 入口"/></Head>
   {current&&<header className="page-header feed-heading"><div><h1>{target?.name||current.name}</h1><p>{current.hint}</p></div></header>}
   {!section&&<Heatmap data={initial.contributions}/>}
   {tagPath&&<div className="breadcrumbs"><Link href={`/${section}`}>全部{current?.name}</Link>{tagPath.split('/').map((_,i)=>{const path=tagPath.split('/').slice(0,i+1).join('/');return <span key={path}> / <Link href={`/${section}/${path}`}>{initial.tags.find(t=>t.path===path)?.name}</Link></span>;})}</div>}