v2.0.0: Add PyPI publish workflow; simplify license field

Add a GitHub Actions workflow (.github/workflows/publish.yml) that builds a wheel and sdist and publishes distributions to PyPI when a release is published. The workflow sets up Python 3.10, installs build tools, builds distributions, and uses pypa/gh-action-pypi-publish with OIDC permissions.

Also simplify the pyproject.toml license entry from a table to a plain string ("MIT").