ci: release with python semantic release

[yeiichi]

Summary

Updates the release workflow so Python Semantic Release owns version bumps, changelog updates, tagging, and GitHub release creation.

Details

• Changes the PyPI workflow from manual tag-triggered publishing to a main-branch release workflow.
• Runs Python Semantic Release after commits land on main.
• Lets PSR update pyproject.toml, update CHANGELOG.rst, create the release commit, create the version tag, and create the GitHub release.
• Publishes to PyPI with Trusted Publishing only when PSR actually creates a release.
• Adds an explicit PSR build command that builds and checks wheel/sdist artifacts.
• Makes RST changelog behavior explicit:
  • mode = "update"
  • changelog_file = "CHANGELOG.rst"
  • output_format = "rst"
  • insertion marker matches the existing CHANGELOG.rst marker.

Testing

Validated locally:

uv run --with pytest pytest
uv run --with python-semantic-release semantic-release --noop version