feat(site): negotiate markdown docs

[chaliy]

What

Add negotiated Markdown representations for Bashkit docs pages.

Why

Docs should be readable by clients that explicitly prefer text/markdown without changing the default browser HTML experience.

How

• Generate /docs.md and /docs/<slug>.md static Markdown assets from the existing curated docs metadata and canonical source markdown.
• Add a Cloudflare Worker that serves Markdown for docs URLs only when Accept explicitly prefers text/markdown, with Vary: Accept for cache correctness.
• Add YAML front matter and generated navigation to negotiated Markdown docs.
• Extend postbuild verification for generated Markdown routes, negotiation helpers, and Markdown docs discovery headers.

Risk

• Low
• Docs routes could serve the wrong representation if Worker routing or Accept parsing regresses; postbuild and Wrangler smoke coverage guard this.

Checklist

• Tests added or updated
• Backward compatibility considered

[cloudflare-workers-and-pages]

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	bashkit	8cf8b77	Commit Preview URL	May 26 2026, 04:26 AM