fix(pages): link CSS that island and Markdown pages reach through components

[Brooooooklyn]

Fixes #452

Problem

pages/layout.tsx ──renders──► src/Shell.tsx ──imports──► src/global.css

vp dev applied global.css. A production build did not:

• The islands client entry was only built when a page or layout file had a direct CSS import, <style> or island import (a text scan). With CSS only reachable through a component, no client build ran, so pages got no <link rel="stylesheet">.
• Even when the entry was built, it only imported the direct CSS imports of pages and layouts.

Fix

server build                                  client build
────────────                                  ────────────
buildEnd: walk static importedIds             islands client entry
  layouts first, then pages     ──recorded──►   import "<css id>"; ...
  (real resolution: aliases,                    ▼
   packages, Vue/Svelte styles)                 islands-client-*.css → <link> on island/md pages

• When the entry is built: for every app with island or Markdown pages (hasIslandPages). It replaces the needsIslandClientBundle text scan, which only the adapters used.
• What CSS goes in:
  • The server build has already resolved every import of the island pages and layouts, so the server build's module graph lists the stylesheets they reach.
  • Static imports only, in import order, like the dev CSS collector. ?inline / ?url / ?raw are skipped.
  • The walk also enters island components, as dev does, so a layout that renders one without hydrating keeps its CSS.
  • Without a server build (client-only builds), the old direct-import scan is still used.
• Framework details:
  • CSS modules (*.module.css, Vue <style module>) are kept. Vite marks them side-effect free, so the bare import would drop them.
  • Vue scoped styles: cssScopeTo is cleared for the recorded ids, because the component itself is not in the client bundle.
  • Svelte: the entry imports vite-plugin-svelte's own ?svelte&type=style id, compiled through the existing island-style loader, so the same rule is not emitted twice in mixed apps.
• No extra JS:
  • Pages that need no JS still get only the <link>, no <script>.
  • With no islands and no page needing JS, the entry holds only the CSS imports, so no hydration runtime is bundled.
  • React and Solid now add the entry to the client build only, as Vue and Svelte already did, so the worker no longer bundles it.

Behaviour changes worth knowing

• Static-output island apps without any direct CSS import are now prerendered. Before, the missing client build meant no HTML.
• A Vue island page or layout with <style scoped> used to fail the build (PARSE_ERROR on ...&scoped=true). It now builds and links the CSS.
• playground/markdown-blog: same CSS rules, but @void/md/theme.css (imported in the script) now comes before the layout's <style>, which is Vue's normal order.

Known limit (unchanged, not in this PR)

In apps with both island and regular pages, collectRouteCss (routing-assets.ts) puts a chunk's own CSS before the CSS of chunks it imports, so the islands stylesheet can come before shared layout CSS. That order already applied to direct page CSS on main. Changing it would change the link order on every page.

Tests

New production-build tests for each adapter (packages/{react,vue,svelte,solid}/test/integration/island-css-build.test.ts, shared test/island-css-build.ts). Each one builds a static app where a layout renders a component that imports CSS, with an island page and a Markdown page, and checks:

• the page links a stylesheet, and each rule (plain CSS, CSS module, Vue/Svelte <style>, Vue scoped with matching data-v-*, Svelte matching svelte-* class) appears exactly once;
• pages that need no JS have no <script>;
• React: an app with no CSS has no link, script or hydrateRoot, and dist/ssr has no islands client.

Plus unit tests for collectIslandStyles and islandStyleRoots (order, no repeats, \0 ids, ?inline/?url).

Check	Result
New build tests on main sources	6 fail (no client build)
New build tests with the fix	pass
Undo each part (walk, entry decision, each adapter hook, CSS-module keep, Vue scope, Svelte id)	a test fails for each
Adapter + md package tests, browser suites with local Chrome	pass
vp fmt --check, vp lint, typecheck void/react/vue/svelte/solid	clean

🤖 Generated with Claude Code

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