feat(search): 站内搜索/RSS/sitemap/Artalk 懒挂载

- astro-pagefind：构建期索引；SearchDialog 首开懒加载 + 200ms 防抖，
  入口=Header 钮 + 键盘 /（P0 键位集补全）
- @astrojs/rss：posts 全量（draft 排除），双语分流留 Phase 3
- @astrojs/sitemap：sitemap-index 产出
- ArtalkComments：IntersectionObserver 进入视口才拉 Artalk.js，
  pageKey=/archives/{slug}/（中英共键，评论不分裂）

验证: pnpm astro build exit 0；dist/pagefind 目录 + rss.xml +
      sitemap-index.xml 三件断言过

Spec: 2026-10-24_add-blog-skeleton
Co-authored-by: GLM-5.3

src/pages/archives/[...slug].astro

@@ -2,6 +2,7 @@
 import type { CollectionEntry } from 'astro:content';
 import { getCollection, render } from 'astro:content';
 import BaseLayout from '../../layouts/BaseLayout.astro';
+import ArtalkComments from '../../components/ArtalkComments.astro';
 import { trackOf } from '../../content.config';
 
 // URL = /archives/{slug}，slug 即文件名，与 Halo 旧结构 1:1（不可改）
@@ -104,8 +105,7 @@ const toc = headings.filter((h) => h.depth === 2 || h.depth === 3);
     )}
   </nav>
 
-  <!-- T8 填充：在此容器注入 Artalk 脚本，data-page-key 即文章 id -->
-  <div id="artalk-container" data-page-key={entry.id}></div>
+  <ArtalkComments pageKey={`/archives/${entry.id}/`} pageTitle={entry.data.title} />
 </BaseLayout>
 
 <script>