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/SearchDialog.astro

@@ -0,0 +1,101 @@
+---
+// 站内搜索（Pagefind）：首次打开才懒加载索引（spectre 模式，见调研报告 §4c）
+// 入口：Header 搜索钮 + 键盘 `/`
+---
+
+<dialog id="search-dialog" class="search-dialog">
+  <input id="search-input" type="search" placeholder="搜索文章…（Esc 关闭）" autocomplete="off" />
+  <ul id="search-results" class="results" aria-live="polite"></ul>
+  <p class="search-hint">索引由 Pagefind 构建期生成 · 静态站零后端</p>
+</dialog>
+
+<script>
+  const dlg = document.getElementById('search-dialog') as HTMLDialogElement;
+  const input = document.getElementById('search-input') as HTMLInputElement;
+  const list = document.getElementById('search-results')!;
+  type PagefindLike = {
+    search: (q: string) => Promise<{ results: { data: () => Promise<{ url: string; excerpt: string; meta: { title: string } }> }[] }>;
+  };
+  let pf: PagefindLike | null = null;
+  let loadStarted = false;
+
+  async function ensureIndex() {
+    if (loadStarted) return;
+    loadStarted = true;
+    pf = (await import(/* @vite-ignore */ '/pagefind/pagefind.js')) as unknown as PagefindLike;
+  }
+
+  function open() {
+    dlg.showModal();
+    input.value = '';
+    list.innerHTML = '';
+    void ensureIndex();
+    input.focus();
+  }
+
+  document.querySelector('[data-search-trigger]')?.addEventListener('click', open);
+  document.addEventListener('keydown', (e) => {
+    const inField = document.activeElement instanceof HTMLElement &&
+      (document.activeElement.tagName === 'INPUT' || document.activeElement.tagName === 'TEXTAREA');
+    if (e.key === '/' && !inField) { e.preventDefault(); open(); }
+  });
+
+  let timer: number | undefined;
+  input.addEventListener('input', () => {
+    clearTimeout(timer);
+    timer = window.setTimeout(async () => {
+      if (!pf) return;
+      const q = input.value.trim();
+      if (!q) { list.innerHTML = ''; return; }
+      const res = await pf.search(q);
+      list.innerHTML = '';
+      for (const r of res.results.slice(0, 8)) {
+        const d = await r.data();
+        const li = document.createElement('li');
+        const a = document.createElement('a');
+        a.href = d.url;
+        a.className = 'tap';
+        a.innerHTML = `<strong>${d.meta.title}</strong><span>${d.excerpt}</span>`;
+        li.appendChild(a);
+        list.appendChild(li);
+      }
+      if (!list.children.length) list.innerHTML = '<li class="empty">无结果</li>';
+    }, 200);
+  });
+</script>
+
+<style>
+  .search-dialog {
+    margin-top: 12vh;
+    width: min(560px, calc(100vw - 32px));
+    border: 1px solid var(--line);
+    border-radius: 10px;
+    background: var(--bg);
+    color: var(--ink-2);
+    padding: var(--space-3);
+  }
+  .search-dialog::backdrop { background: rgba(0, 0, 0, 0.45); }
+  input[type='search'] {
+    width: 100%;
+    padding: var(--space-2) var(--space-3);
+    border: 1px solid var(--line);
+    border-radius: 8px;
+    background: var(--bg-soft);
+    font-size: 15px;
+  }
+  .results { list-style: none; padding: 0; margin: var(--space-2) 0 0; max-height: 50vh; overflow-y: auto; }
+  .results a {
+    display: flex;
+    flex-direction: column;
+    gap: 2px;
+    padding: var(--space-2) var(--space-3);
+    border-radius: 8px;
+    text-decoration: none;
+  }
+  .results a:hover { background: var(--bg-soft); }
+  .results strong { color: var(--ink-1); font-size: 14px; }
+  .results span { font-size: 12px; color: var(--ink-3); }
+  .results a span :global(mark) { background: var(--accent-soft); }
+  .empty { padding: var(--space-3); font-size: 13px; color: var(--ink-3); }
+  .search-hint { margin-top: var(--space-2); font-size: 11px; color: var(--ink-4); text-align: center; font-family: var(--font-mono); }
+</style>