Docs: prototype versioned reference microfrontend

[Blargian]

Summary

• Prototype snapshot-driven reference navigation, rendering, settings explorers, route audit, and archive tooling.
• Add a standalone Vercel reference-docs microfrontend scaffold.
• Render Head from a private Cloudflare R2 snapshot fetched during the Vercel build. Serve archived release bodies from the R2 sites/version/locale object-storage contract at request time.
• When no R2 origins are configured, render an explicit unavailable state rather than fixture documentation.

Validation

• pnpm typecheck
• pnpm --dir reference-docs test
• pnpm --dir reference-docs check
• pnpm --dir reference-docs build without R2 configuration

Follow-up

• Provision the private Head snapshot R2 build input and public R2 sites archive origin, then connect this microfrontend project in Vercel.

[github-actions]

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Preview	Deployment	Components	Updated (UTC)
Docs preview	🔴 Failed	English: 🟡 Building; translations: Production fallback	2026-09-28 16:29 UTC