v0.1.0: Add PyPI publishing setup

- Complete pyproject metadata: authors, keywords, classifiers, project
  URLs, PEP 639 license declaration (SPDX MIT + license-files)
- Add GitHub Actions workflow that builds sdist/wheel and publishes to
  PyPI via Trusted Publishing when a release is published
- Verified locally: build succeeds, wheel installs on Python 3.12,
  entry point and metadata check out