Draft: llms.txt generator + multi-tier artifacts

[albertocavalcante]

I don't expect this to be merged - this PR is only to show the concept and link to bazelbuild/bazel#27654

Summary

• add scripts/generate_llms.py to emit llms.txt, abridged/compressed variants, and per-section corpora directly from Mintlify navigation
• document how to regenerate / preview the files and make the outputs reproducible via env + CLI knobs
• ignore llms*.txt in git so contributors run the generator instead of checking in megabyte-scale artifacts

Notes

• This is a draft PR to show the concept and gather early feedback.
• Generated files live at the repo root after running python3 scripts/generate_llms.py and can be previewed with mint dev (http://localhost:3000/llms.txt).

Testing

• python3 scripts/generate_llms.py
• mint dev