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/DocsSiteTitle.astro

@@ -0,0 +1,54 @@
+---
+import Mark from '../assets/placeholder-mark.svg?raw';
+import { brand } from '../lib/brand.mjs';
+
+/**
+ * Overrides Starlight's `SiteTitle` so the documentation header carries the same lockup as
+ * the marketing header. One product, two chromes, one mark.
+ *
+ * It exists because Starlight's `logo` option renders an `<img>`, and our mark is an
+ * inline-only asset: it is drawn in `currentColor` so it inherits `--gold` and follows a
+ * bind-mounted `theme.css` for free (§7). An SVG loaded through `<img>` is an independent
+ * document — `currentColor` has nothing to inherit from there, and the mark renders black
+ * on black. Inlining it is what makes the token reach the artwork.
+ *
+ * Phase 2 replaces the placeholder with the real emblem derivatives; this component keeps
+ * working, because what it needs is markup rather than a file.
+ */
+const { siteTitle, siteTitleHref } = Astro.locals.starlightRoute;
+---
+
+<a href={siteTitleHref} class="site-title sl-flex">
+  <span class="docs-mark" set:html={Mark} aria-hidden="true" />
+  <span translate="no">{siteTitle || brand.siteName}</span>
+</a>
+
+<style>
+  /* Layout only. The brand of this element — display face, weight, letter-spacing and
+     colour — is set once in src/styles/starlight.css, next to the rest of the docs
+     theming, so there is one place to change it. */
+  .site-title {
+    align-items: center;
+    gap: 0.6rem;
+    font-size: var(--sl-text-h4);
+    text-decoration: none;
+    white-space: nowrap;
+    min-width: 0;
+  }
+
+  .docs-mark {
+    display: inline-flex;
+    flex: none;
+    width: 30px;
+    height: 30px;
+    color: var(--gold);
+  }
+
+  :global(:root[data-theme='light']) .docs-mark {
+    color: var(--light-gold);
+  }
+
+  span:last-child {
+    overflow: hidden;
+  }
+</style>