- bump version to 0.3.0
- add the 0.3.0 changelog entry (first PyPI release of the fork),
  folding the previously unreleased notes into it
- add `make publish`: builds and uploads via uv, reading the PyPI API
  token from the gitignored .pypi-token file; refuses to run while the
  placeholder is in place

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>