Add gh-release Makefile target for PyPI publishing

[lbliii]

Summary

• Adds make gh-release target that creates a GitHub release from site/content/releases/{version}.md, which triggers the existing python-publish.yml workflow to publish to PyPI
• Reads version and project name from pyproject.toml, strips YAML frontmatter from release notes, and pushes the version tag before creating the release
• Matches the pattern used in other b-stack repos (chirp, bengal)

Test plan

• Verify make help displays the new gh-release target
• Run make gh-release after tagging a test version to confirm end-to-end flow

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