Add environment variables for fine-grained control over TTS rate limiting
and Better Auth behavior. Move documentation to external Docusaurus site
with automated deployment workflows.
- TTS rate limiting can now be enabled/disabled via TTS_ENABLE_RATE_LIMIT
- Customizable daily limits for anonymous/authenticated users and IP backstops
- Better Auth rate limiting can be disabled via DISABLE_AUTH_RATE_LIMIT
- Rename library import env vars to IMPORT_LIBRARY_DIRS/DIR
- Add docs-site with Docusaurus and GitHub Actions workflows
- Update README to reference external documentation
