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/components/ArtalkComments.astro

@@ -0,0 +1,43 @@
+---
+// Artalk 评论挂载（Phase 0 已部署 @ https://wait4x.online/artalk）
+// 懒加载：进入视口才拉 Artalk.js，长文页不为其付首屏成本
+interface Props {
+  pageKey: string;   // 评论流键：中英双语页共用同一 slug（评论不分裂）
+  pageTitle: string;
+}
+const { pageKey, pageTitle } = Astro.props;
+---
+
+<div id="artalk-container" data-page-key={pageKey} data-page-title={pageTitle}></div>
+
+<script>
+  const el = document.getElementById('artalk-container');
+  if (el) {
+    const mount = () => {
+      if (document.getElementById('artalk-lib')) return initArtalk();
+      const s = document.createElement('script');
+      s.id = 'artalk-lib';
+      s.src = 'https://wait4x.online/artalk/dist/Artalk.js';
+      s.onload = initArtalk;
+      document.head.appendChild(s);
+    };
+    const initArtalk = () => {
+      const lib = (window as unknown as { Artalk?: { init: (o: object) => void } }).Artalk;
+      lib?.init({
+        el: '#artalk-container',
+        server: 'https://wait4x.online/artalk',
+        site: 'wait4x',
+        pageKey: el.dataset.pageKey,
+        pageTitle: el.dataset.pageTitle,
+        locale: 'zh-CN',
+      });
+    };
+    // 进入视口 ~200px 前挂载；无 IO 环境直接挂
+    if ('IntersectionObserver' in window) {
+      new IntersectionObserver(
+        (entries, obs) => { if (entries.some((e) => e.isIntersecting)) { obs.disconnect(); mount(); } },
+        { rootMargin: '200px' }
+      ).observe(el);
+    } else mount();
+  }
+</script>