refactor(docs): use shared @unom/app-ui/footer component

The docs footer was a hand-maintained mirror of the marketing site's. Both now
render the same @unom/app-ui/footer component, so they stay in sync. The shared
view themes itself through @unom/style tokens (which the docs already map onto
their Fumadocs surfaces), and a resolveHref hook rebases root-relative links
onto the marketing-site origin. Footer types now come from the library too.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs-site/package.json

@@ -14,6 +14,7 @@
     "@scalar/api-reference-react": "^0.9.47",
     "@tanstack/react-router": "^1.121.0",
     "@tanstack/react-start": "^1.121.0",
+    "@unom/app-ui": "^0.1.0",
     "@unom/style": "^0.4.4",
     "@unom/ui": "^0.8.16",
     "fumadocs-core": "^16.10.5",