feat: add Markdown versions of public pages

[celeroncoder]

What changed

• serve Markdown versions at /.md, /index.md, /blog.md, and /blog/.md
• convert Payload Lexical blog content to Markdown, including fenced code blocks
• advertise each Markdown page with a text/markdown alternate link
• keep homepage Markdown in sync through shared portfolio content
• return Markdown 404 and 500 responses with the correct content type

Verification

• ./node_modules/.bin/tsc --noEmit
• ./node_modules/.bin/next build
• HTTP check confirmed .md rewrites return text/markdown and Markdown error bodies

[vercel]

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Project	Deployment	Actions	Updated (UTC)
celeroncoder-web	Ready	Preview	Aug 23, 2026 4:21pm

[github-actions]

React Doctor found 1 new issue in 1 file · 1 warning · score 92 / 100 (Great) · 0 fixed · vs master

1 warning

lib/markdown-pages.ts

• ⚠️ L15 Intl formatter rebuilt each call js-hoist-intl

_{Reviewed by React Doctor for commit c6e99c7. See inline comments for fixes.}