First release

docs: publish the documentation site to GitHub Pages

MkDocs Material site built from the existing docs/ markdown, deployed by
.github/workflows/docs.yml on pushes to main (pull requests build but do
not deploy). Built with --strict, so a broken internal link or an orphan
page fails CI.

mkdocs-callouts renders the GitHub-style '> [!NOTE]' alerts as Material
admonitions, so the same markdown reads correctly on github.com and on
the site.

Links the site from pyproject ([project.urls] Homepage + Documentation,
so PyPI shows it) and from the README (badges + docs table).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ETGoz8ozsPNUr3K2MwpAnm