docs: Migrate docs site to @vercel/geistdocs package
Replace the locally-vendored geistdocs runtime in apps/docs with the
published @vercel/geistdocs package, keeping site-specific content,
routes, and product UI local as thin package-backed adapters.
Adopted from the package:
- Docs page via createDocsPage (MobileDocsBar, page actions, feedback)
- Docs/home layouts, provider, OSS navbar, search and Ask AI routes
- Per-page markdown (llms.mdx), sitemap.md, new agents.md, proxy with
AI-agent rewrites and markdown negotiation
- MDX component defaults, design tokens via package styles.css
Kept custom (deliberate deviations):
- Curated /llms.txt index and /llms-full.txt (public contract)
- HMAC-signed OG images, rss/feed.xml, robots, Redis crawler sitemap
- Four-column footer (Fides cookie link), versioned-docs banner via the
sidebarTop slot, RemoteCacheCounter via page-action extras
- PackageManagerTabs, reactflow diagram system, heading-badge pipeline
Version alignment: next 16.2.6 (exact peer pin), fumadocs-core/ui
16.2.2, fumadocs-mdx 14.0.4, fumadocs-openapi 10.2.7. Removed ~20
dependencies owned by deleted vendored code.
Site components written against Tailwind default palettes were
translated to the Geist scale (the package remaps gray/blue/red/green
etc. to --ds-* tokens, which are much lighter at the same step).
.npmrc: hoist tailwindcss so the package styles.css can resolve its
internal @import under this repo's restricted hoist-pattern list.
