docs: mkdocs GitHub Pages deploy

[stefan-jansen]

Summary

• Add GitHub Pages deploy workflow (docs.yml) — builds on push to main, deploys via actions/deploy-pages
• Update nav in mkdocs.yml to include all 8 user guide pages (was missing 5)
• Replace Sphinx deps with mkdocs-material + mkdocstrings in pyproject.toml
• Pin mkdocs<2 (Material not yet compatible with MkDocs 2.0)
• Fix broken links in ml-readiness.md
• Add site/ to .gitignore

Test plan

• mkdocs build --strict passes locally
• CI passes (lint, typecheck, tests)
• After merge, docs workflow deploys to GitHub Pages

Note: GitHub Pages needs to be enabled in repo settings (Settings > Pages > Source: GitHub Actions) before the deploy will work.

[Copilot]

Pull request overview

Adds an automated MkDocs-based documentation deployment to GitHub Pages and updates documentation configuration/links to match the new docs site location.

Changes:

• Replace Sphinx tooling with MkDocs Material + mkdocstrings in project extras.
• Update MkDocs config/nav and fix a couple of internal docs links.
• Add a GitHub Actions workflow to build and deploy docs to GitHub Pages.

Reviewed changes

Copilot reviewed 4 out of 6 changed files in this pull request and generated 3 comments.

File	Description
pyproject.toml	Swaps docs dependencies to MkDocs stack and updates the published documentation URL.
mkdocs.yml	Adjusts site/repo URLs and expands nav to include all user guide pages.
docs/user-guide/ml-readiness.md	Fixes internal links to point at the correct pages under MkDocs.
.github/workflows/docs.yml	Adds CI workflow to build MkDocs site and deploy via GitHub Pages actions.

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