Migrate documentation to Great Docs

[uriahf]

What changed

• migrate the documentation configuration from quartodoc/Quarto to Great Docs
• move the Getting Started guide into user_guide/
• organize the documented public API into performance-data, discrimination, calibration, and utility groups
• include the existing classification and time-to-event APIs
• add a dedicated docs dependency group so package support remains Python >=3.9 while docs build on Python 3.11
• separate package CI from documentation publishing
• publish production documentation to the existing gh-pages root
• deploy pull-request previews under pr-preview/pr-<number>/
• preserve PR preview directories during production documentation deployments
• style Great Docs with the rtichoke-blog palette and typography, including its bundled heading font
• remove obsolete quartodoc documentation infrastructure after migrating its useful content

Scope

This PR only migrates documentation infrastructure and content. It does not implement or redesign create_summary_report(); its source remains unchanged from main.

Validation

• package tests pass
• Ruff checks pass
• the full Great Docs build passes
• all 21 configured API pages render, including 8 time-to-event APIs
• all Python examples from rtichoke-blog render successfully against this branch
• PR preview deployment passes and serves the custom stylesheet and bundled font
• production documentation remains configured for https://uriahf.github.io/rtichoke_python/
• PR preview: https://uriahf.github.io/rtichoke_python/pr-preview/pr-282/

[github-actions]

PR Preview Action v1.8.1
Preview removed because the pull request was closed.
2026-08-10 19:14 UTC

[uriahf]

Looks good