Release the gist Python package

Release the gist Python package

The package version comes from the git tag through uv-dynamic-versioning. pyproject.toml declares dynamic = ["version"] and the distribution name gist-linkml, because the PyPI name gist belongs to an unrelated project (kracekumar/gist). The import package is still gist. No file is bumped on release.

1. Once, before the first release, push the v0.1.0 baseline tag on main. Both jobs of .github/workflows/semantic-release.yml refuse to release without a v* tag, because semantic-release would otherwise make the first release 1.0.0. The baseline is not uploaded anywhere.
2. Write the change under ## [Unreleased] in CHANGELOG.md, and type the commit and the pull-request title feat:, fix: or security:, or mark any type breaking with a !. A BREAKING CHANGE footer marks a commit breaking too. Other types release nothing. The plan job refuses a releasing pull request whose changelog section is empty or whose title carries no releasing type.
3. Merge to main. The release job, in the release Environment, retitles the section ## [X.Y.Z] - YYYY-MM-DD, commits CHANGELOG.md, tags vX.Y.Z and publishes the GitHub Release from that text. While below 1.0.0, .releaserc.json makes a breaking change a minor bump.
4. Once the PYPI_RELEASE_ENABLED repository variable is true, the same job dispatches .github/workflows/pypi-publish.yaml on the new tag, which builds with uv build and uploads to PyPI through trusted publishing in the pypi-release environment (https://pypi.org/p/gist-linkml). PyPI accepts the first upload only once a pending trusted publisher for gist-linkml naming that workflow and environment is registered there.

With the variable on, a v* tag that a person pushes uploads to TestPyPI instead, unless it is the baseline, and a release published by hand in the GitHub UI uploads to PyPI. With it unset, pypi-publish.yaml skips every trigger.

PyPI releases are off for now, and nothing is on PyPI or TestPyPI.

Every release also gets the LOKF copy of gist_core.yaml, whatever PYPI_RELEASE_ENABLED says. The release job dispatches .github/workflows/lokf-copy-release.yaml on the new tag, and that workflow attaches the copy to the GitHub Release as gist-linkml-lokf-<tag>.yaml, with a .sha256 checksum.