feat(site): phase 1 — the foundation

Astro 7 with the Node adapter, Starlight mounted at /docs, the token file, both
self-hosted typefaces, the layout shell, and the two build-time checks from §12.

The palette's gold and cyan are sampled from runic-emblem.png rather than
guessed, per §11: 494,059 opaque pixels binned by hue, each value annotated with
its measured contrast against the ground, and restricted rather than brightened
where a ratio fails.

- checkTokens.mjs fails the build on any colour literal outside tokens.css,
  which is what keeps §7's "recolouring is a file copy" promise true.
- checkFacts.mjs re-reads all 14 externally-sourced facts from their authorities
  over the Gitea API and fails on disagreement. It also enforces D13: no email
  address in the source outside brand-default/brand.json.
- Both were negative-tested; neither has ever been allowed to pass by default.

§6 asks for output:'server' with per-page prerender=true. Astro 7 expresses the
same runtime shape as output:'static' with an adapter, opting individual routes
out — so the default is static rather than accidentally server-rendered.

Co-Authored-By: Claude <noreply@anthropic.com>

src/components/Header.astro

@@ -0,0 +1,49 @@
+---
+import { brand } from '../lib/brand.mjs';
+import Mark from '../assets/placeholder-mark.svg?raw';
+
+/**
+ * The marketing header. The docs get Starlight's own header, themed to match in
+ * `src/styles/starlight.css` — one site, two chromes, the same lockup.
+ *
+ * The nav names the routes §10 specifies. Phase 3 onwards fills them in; a link added
+ * here before its page exists fails `checkLinks.mjs`, which is the order we want.
+ */
+const { pathname } = Astro.url;
+
+const links = [
+  { href: '/features/', label: 'Features' },
+  { href: '/docs/', label: 'Docs' },
+  { href: '/app/', label: 'App' },
+  { href: '/community/', label: 'Community' },
+];
+
+const isCurrent = (href: string) =>
+  href === '/' ? pathname === '/' : pathname.startsWith(href);
+---
+
+<header class="site-header">
+  <div class="page site-header__inner">
+    <a class="brand-lockup" href="/">
+      <span class="brand-lockup__mark" set:html={Mark} />
+      <span class="brand-lockup__name">{brand.siteName}</span>
+    </a>
+
+    <nav class="site-nav" aria-label="Primary">
+      {
+        links.map((link) => (
+          <a href={link.href} aria-current={isCurrent(link.href) ? 'page' : undefined}>
+            {link.label}
+          </a>
+        ))
+      }
+    </nav>
+  </div>
+</header>
+
+<style>
+  .brand-lockup__mark {
+    display: inline-flex;
+    color: var(--gold);
+  }
+</style>