feat(docs): add llms.txt generation for LLM-friendly documentation

[rororowyourboat]

Summary

Add llms.txt and llms-full.txt generation to the MkDocs docs build, following the llmstxt.org standard. This makes our documentation discoverable and consumable by LLMs and AI coding tools.

Motivation

• llms.txt is an emerging standard (844k+ sites) for providing structured, LLM-friendly documentation
• Major projects (Anthropic, Cloudflare, Stripe, LangChain) already ship it
• Our 161 docs pages across 7 packages are a perfect fit — the index gives LLMs a curated overview, while the full file gives deep context

Plan

Plugin: mkdocs-llmstxt (v0.5.0, by pawamoy)

• Renders HTML→Markdown so it correctly captures mkdocstrings-generated API docs
• Auto-discovers sections from existing MkDocs nav structure

Changes:

1. pyproject.toml — add mkdocs-llmstxt>=0.5 to [dependency-groups] docs
2. mkdocs.yml — add llmstxt plugin with markdown_description and full_output: llms-full.txt

Output:

• /llms.txt — curated index with links + descriptions (< 10KB)
• /llms-full.txt — all 161 pages expanded inline (full content)

Both files auto-generated on every mkdocs build and served on the deployed site.

[rororowyourboat]

Resolved by PR #79 — mkdocs-llmstxt plugin generates /llms.txt and /llms-full.txt on every build. Follow-up commit added descriptions and removed outdated design docs from the index.