feat: add CI, Docker, auth, typed API client, shiki code blocks, e2e tests

- CI: GitHub Actions (bun 1.3.14, lint/typecheck/test/build/format gates)
- Docker: multi-stage standalone build + .dockerignore (next.config output=standalone)
- Auth: better-auth server (memory adapter, drizzle-swap-ready) + react client
  + /api/auth/[...all] route handler
- API: /api/health + /api/openapi routes, openapi-typescript codegen to
  types/api.ts, typed openapi-fetch client (lib/api, lib/http)
- Shiki: server-side CodeBlock component (escaped HTML)
- E2E: playwright home + health specs on dedicated :3100 (chromium 1243
  installed from GCS after CDN timeout)
- Dev: allow 127.0.0.1/localhost dev origins (HMR for local tooling)

components/ui/code-block.tsx

@@ -0,0 +1,24 @@
+import { codeToHtml } from "shiki";
+
+const DEFAULT_THEME = "github-dark";
+
+export async function CodeBlock({
+  code,
+  lang = "text",
+  theme = DEFAULT_THEME,
+  className,
+}: {
+  code: string;
+  lang?: string;
+  theme?: string;
+  className?: string;
+}) {
+  const html = await codeToHtml(code, {
+    lang,
+    theme,
+  });
+
+  // Safe: shiki escapes all input before emitting HTML (no raw user content
+  // reaches innerHTML), so no sanitizer is required here.
+  return <div className={className} dangerouslySetInnerHTML={{ __html: html }} />;
+}