Add LLM site files

[djalmaaraujo]

Summary

• add routed /llms.txt, /llms-full.txt, and /sitemap.xml responses for the docs app
• centralize generated content in SiteFiles and add site_files:generate for refreshable static copies
• update robots.txt to advertise the sitemap and cover the routes with controller tests

Tests

• bundle exec rails test test/controllers/site_files_controller_test.rb (Docker Ruby 3.4.7)
• git diff --check

Fixes #345

[djalmaaraujo]

Update: added committed static copies in docs/public/ for /llms.txt, /llms-full.txt, and /sitemap.xml, generated from the same SiteFiles source. This keeps the routed responses and makes deploy/CDN static serving work without needing the Rails route to be hit first.

Validation added locally:

• public files match SiteFiles generator output
• public sitemap parses as XML
• git diff --check

[djalmaaraujo]

Update: documented the generation flow in docs/README.md and added docs/CLAUDE.md with the instruction to update SiteFiles and run bin/rails site_files:generate whenever public routes/controllers/views add, remove, or rename URLs.

Validation: git diff --check.