feat: add llms.txt endpoint for LLM-optimized documentation

[quantizor]

Add /llms.txt endpoint that serves a concatenated, text-only version of all Tailwind CSS documentation pages optimized for Large Language Model consumption.

• Extract text from MDX files, removing JSX components and preserving code blocks
• Remove standalone HTML blocks (not in code blocks)
• Extract meaningful content from custom components (ApiTable, ResponsiveDesign, etc.)
• Statically generate the output at build time
• Include all 185 documentation files in proper order with sections

:)

[vercel[bot]]

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[quantizor]

@petersuhm 👋

[quantizor]

As a future enhancement, I'd like to introduce the markdown-to-jsx AST parser https://github.com/quantizor/markdown-to-jsx/pull/725 when it's ready so we can get rid of the gnarly regexes.

[quantizor]

Now that v9 is out, I'll refactor this PR tonight.

[quantizor]

@reinink this is ready to be reviewed