Consider `llms.md`, instead

Since it's Markdown, consider using `llms.md`, instead. This will hint to viewers to syntax highlight, allow rendered previews, etc.

Start by reading how the repository currently uses llms.txt and compare that convention with the proposed llms.md filename. Check the repository references and generated or published entry points, then confirm that the chosen filename is used consistently and that the Markdown benefits described in the issue are preserved.

Written by the indexing model from the issue text.