feat(structure): compact archive + tag pages + hero/featured, and fix site search

Found a real bug while verifying the nav search: /pagefind/pagefind.js is an ES
module that defines no window.Pagefind, but Search.astro loaded it with a classic
<script src> and read window.Pagefind — so every query answered "Search is
unavailable." (confirmed live before the fix). Now a dynamic import; the specifier
must be a variable or Rollup resolves it at build time and the build fails.

Measured before/after in a real browser:

- archive /posts/ + /zh/posts/: 18,220px -> 3,788px (71 rows at 44px, grouped by
  year) with a client-side filter (title/tags/description text, category chips,
  14 tag chips, zero requests). Tested: "nginx" -> 6 rows, chip devops -> 28.
- tag pages for tags with >= 3 posts. Measured 235 distinct tags (an earlier brief
  claimed 74), 156 used exactly once — pages only where a topic exists: 40 tags ->
  80 pages, build 165 -> 245 pages. Pills link only when a page exists.
- homepage + ZH homepage: hero (288px) with the real scale claim, three CTAs, a
  fixed Featured 4 (scale -> automation -> observability -> a delivered result),
  Latest 10 -> 6. ZH hero had linked "关于我" to the English /about/.
- long code blocks collapse above 420px with an Expand button + gradient, copy
  button still copies the whole block (verified on the 1010px block).
- search is visible ("⌕ Search /" pill, "/" plus the existing Ctrl/Cmd+K) and the
  zero-result screen offers topic chips instead of a dead end.

Docs: project-state B3 entry, ops-runbook Pagefind gotcha.

src/components/Search.astro

@@ -11,6 +11,13 @@ const placeholder =
   lang === 'zh' ? '搜索文章…' : 'Search posts…';
 const noResults =
   lang === 'zh' ? '没有匹配的结果。' : 'No results.';
+// Empty-search state: a dead end helps nobody. Offer the topic entry points that
+// actually exist (tag pages are generated for tags with >= 3 posts).
+const popular = ['docker', 'self-hosting', 'nginx', 'monitoring', 'automation'];
+const popularHref = (t: string) => (lang === 'zh' ? `/zh/tags/${t}/` : `/tags/${t}/`);
+const tryLabel = lang === 'zh' ? '试试这些主题：' : 'Try a topic:';
+const archiveLabel = lang === 'zh' ? '浏览全部文章' : 'Browse all posts';
+const archiveHref = lang === 'zh' ? '/zh/posts/' : '/posts/';
 ---
 
 <div class="search-overlay" id="search-overlay" hidden>
@@ -28,6 +35,16 @@ const noResults =
     </div>
     <div class="search-results" id="search-results"></div>
   </div>
+
+  <!-- Dead-end screen for a search with no hits: real links, rendered at build time. -->
+  <template id="search-empty-tpl">
+    <p class="excerpt" data-role="message">{noResults}</p>
+    <p class="excerpt" data-role="try">{tryLabel}</p>
+    <p class="search-empty-chips">
+      {popular.map((t) => <a class="chip" href={popularHref(t)}>{t}</a>)}
+      <a class="chip" href={archiveHref}>{archiveLabel}</a>
+    </p>
+  </template>
 </div>
 
 <style>
@@ -88,6 +105,17 @@ const noResults =
   .search-result:hover { color: var(--brand); }
   .search-result h3 { margin: 0 0 0.2rem; font-size: 1.05rem; }
   .search-result .excerpt { color: var(--muted); font-size: 0.88rem; margin: 0; }
+  .search-empty-chips { display: flex; flex-wrap: wrap; gap: 0.4rem; margin-top: 0.5rem; }
+  .search-empty .chip {
+    color: var(--muted);
+    background: var(--surface);
+    border: 1px solid var(--border);
+    border-radius: 999px;
+    padding: 0.22rem 0.6rem;
+    font-size: 0.78rem;
+    text-decoration: none;
+  }
+  .search-empty .chip:hover { color: var(--brand); border-color: var(--brand); }
   .search-result mark {
     background: color-mix(in srgb, var(--brand) 25%, transparent);
     color: var(--ink);
@@ -140,17 +168,17 @@ const noResults =
 
   async function loadPagefind() {
     if (pagefind) return pagefind;
-    // Pagefind's UI/JS is copied into /pagefind/ post-build. Load it via a
-    // script tag (not a dynamic import) so Vite leaves the URL untouched.
-    await new Promise<void>((resolve, reject) => {
-      const s = document.createElement('script');
-      s.src = '/pagefind/pagefind.js';
-      s.onload = () => resolve();
-      s.onerror = () => reject(new Error('pagefind load failed'));
-      document.head.appendChild(s);
-    });
-    const w = window as unknown as { Pagefind?: Pagefind };
-    pagefind = w.Pagefind;
+    // /pagefind/pagefind.js is copied into the build post-build. It is an **ES module**
+    // (`export { search, debouncedSearch, … }`) and defines NO window global, so loading
+    // it with a classic <script src> leaves window.Pagefind undefined and every search
+    // answered "Search is unavailable." — which is what happened between the search
+    // shipping and this fix. Import it as a module instead; @vite-ignore keeps Vite from
+    // trying to resolve a path that only exists in dist/.
+    // The specifier must be a VARIABLE: Rollup resolves a literal dynamic-import path
+    // at build time (and @vite-ignore does not stop it), which breaks the build because
+    // /pagefind/ only exists in dist/ after the index is generated.
+    const url = '/pagefind/pagefind.js';
+    pagefind = (await import(/* @vite-ignore */ url)) as unknown as Pagefind;
     return pagefind;
   }
 
@@ -169,10 +197,11 @@ const noResults =
         const res = await search;
         results.innerHTML = '';
         if (!res.results.length) {
-          const empty = document.createElement('p');
-          empty.className = 'excerpt';
-          empty.textContent = 'No results.';
-          results.appendChild(empty);
+          // Clone the build-time template: the links cannot drift from the pages that
+          // actually exist (tag pages are only generated for tags with >= 3 posts).
+          results.innerHTML = '';
+          const tpl = document.getElementById('search-empty-tpl') as HTMLTemplateElement | null;
+          if (tpl) results.appendChild(tpl.content.cloneNode(true));
           return;
         }
         for (const r of res.results.slice(0, 12)) {