Deploy auths-docs (Next.js) — site is not live anywhere

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Current state

• main (3833c91) builds clean (bun run type-check && bun run build, all pages prerender) and the content has been reconciled with the real 0.1.2 CLI: leaked sk_test key removed, sidebar examples rewritten to real commands, trust pin syntax, auths-dev branding, honest 🚧 stubs.
• But the app is not deployed: docs.auths.dev currently serves the mkdocs site from the main auths repo, and there is no Vercel project for this repo (auths-docs.vercel.app is 404, no .vercel/ config, no deploy workflow).

To do

1. Create a Vercel project for auths-dev/auths-docs (framework: Next.js; install bun install, build bun run build), production branch main.
2. Decide the domain story — either:
   • point docs.auths.dev at this project (and decide what happens to the mkdocs site), or
   • give this app its own subdomain and keep mkdocs where it is.
     (auths.dev zone is on Vercel DNS, so a CNAME/alias is a one-liner.)
3. Smoke-check after first deploy: /, /docs/quickstart, /docs/authentication, /docs/reference/cli all 200; homepage CTA points at /docs/quickstart.
4. Once subpages are live, the CLI's parked deep links (AU-6) can be restored to point at real URLs.