chore: Prepare Python keymaster for PyPI

[macterra]

Summary

• add PyPI-ready metadata for the archon-keymaster package
• add package-local license, manifest, and publishing checklist
• update install docs for public PyPI installs while preserving editable install guidance
• record the repo instruction that package prep may build/check artifacts but must not upload unless explicitly requested

Validation

• built wheel and sdist locally with python -m build
• twine check /tmp/archon-keymaster-dist/* passed
• installed the built wheel into a clean venv and smoke-tested keymaster --help
• verified the CLI parser still exposes 132 commands
• pytest -q tests from python/keymaster passed: 140 passed

No TestPyPI or PyPI upload was performed.