feat(bankai): Phase 4 follow-ups — css convention, live titles, prerender, HTTP/2, size budget

- style.css convention: <entry dir>/style.css is imported by the virtual
  client entry (CSS is a client concern; server code never sees it — the
  v8 answer to sheetify), extracted and hashed by Vite, stylesheet-linked
  in the head and preloaded via Early Hints. Counter example styled.
- SSR <title> from state: the server reads the first stream chunk before
  writing the head, by which point stores and the first render slice have
  run — DOMTitleChange emits land in the document title. Counter emits.
- bankai build --prerender /,/about renders routes through the same
  toStream path to static <route>/index.html (precompressed, precached
  by the service worker, served with Early Hints).
- bankai serve --h2: HTTP/2 with a generated local cert (openssl,
  cached; allowHTTP1) — browsers only act on Early Hints over h2/h3.
  Tested with a real h2 client observing the 103 interim response.
- npm run size: the framework wire-size budget, enforced in CI. Whole
  framework (core + html engine + morph + hydrate) is 7.97 kB min+gzip /
  7.15 kB brotli; budget 8.5 kB with the v7 '4kb' context documented
  (that number excluded the html engine, which lived in the browserify
  transform).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014NgfSjHE11oFpoSnLVKLXd

examples/counter/style.css

@@ -0,0 +1,29 @@
+/* The style.css convention: bankai's client entry imports this file
+   automatically (CSS is a client concern — server code never sees it),
+   Vite extracts and hashes it, and the server preloads it via Early
+   Hints. The v8 answer to sheetify. */
+
+body {
+  font-family: system-ui, sans-serif;
+  max-width: 36rem;
+  margin: 4rem auto;
+  padding: 0 1rem;
+  line-height: 1.5;
+}
+
+h1 {
+  font-size: 1.6rem;
+}
+
+button {
+  font: inherit;
+  padding: 0.4rem 1.2rem;
+  border: 2px solid currentColor;
+  border-radius: 4px;
+  background: transparent;
+  cursor: pointer;
+}
+
+button:hover {
+  background: #ffc0cb55;
+}