Serve markdown indexes for the docs root and section hubs to agents

[philip]

Summary

• Agents and Accept: text/markdown requests to the docs root (/docs and /docs.md) now receive the curated llms.txt index instead of a redirect or 404. Browsers still land on /docs/introduction.
• Appending .md to a top-level section root (faqs, guides, branching, programs, use-cases, postgresql) now returns a markdown listing of that section's pages, so "append .md to any URL" holds for hubs too.
• Fixed the markdown path and canonical URL for programs and use-cases pages, which were previously served under an incorrect path.
• Non-page content (shared includes, READMEs, templates) is no longer emitted as standalone markdown, making markdown and HTML behavior consistent.
• Internal: de-duplicated shared content helpers; no behavior change.

Test plan

• /docs with Accept: text/markdown and with an agent User-Agent returns the llms.txt index; a browser is redirected to /docs/introduction.
• /docs.md and the section .md indexes return markdown listings.
• programs/use-cases pages resolve as markdown at their correct URLs.
• Unit suites pass; markdown URL QA suite passes against the preview deploy.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
neon-next	Ready	Preview, Comment	Jun 1, 2026 8:11pm