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.

docs/ops-runbook.md

@@ -32,6 +32,14 @@ Markdown (src/content/posts) → Astro build (dist/) → Gitea Actions → act_r
 
 ## Build pitfalls (from prior Astro work — check these first)
 
+- **Pagefind is an ES module and exposes no window global.** `dist/pagefind/pagefind.js`
+  ends with `export { search, debouncedSearch, … }`. Load it with a dynamic `import()`, never
+  a classic `<script src>` + `window.Pagefind` — that combination silently made every search
+  answer "Search is unavailable." for as long as the overlay existed. The specifier must be a
+  **variable** (`const url = '/pagefind/pagefind.js'; await import(/* @vite-ignore */ url)`)
+  because Rollup resolves a literal dynamic-import path at build time and fails on a file that
+  does not exist until after the search index is generated.
+
 - **No JSX helper components in frontmatter** — inline JSX directly in `.map()` calls, or the build fails with `Expected ">" but found "class"`.
 - **Import depth** — `src/pages/*.astro` use `../layouts/…`; subdirs use `../../`. Wrong level = `Could not resolve`.
 - **Footer must render AFTER `<main>`** — a shared header+footer component renders footer above content otherwise.