Test PyPI yank capability via org secret

[nwoodruff-co]

Summary

This adds a temporary workflow_dispatch workflow to test whether the PYPI org secret has sufficient permissions to yank old versions.

• Attempts to yank policyengine-uk==0.35.0 (a very old, unused version) as a probe
• Uses twine yank with __token__ auth via secrets.PYPI
• If yank succeeds, the org secret has full write access (publish + yank); if it fails with a 403/auth error, it is publish-only or scoped differently
• The yank itself is benign — 0.35.0 is ancient and not in use

Test plan

• Run the workflow_dispatch workflow manually from the Actions tab after merging/on this branch
• Check the logs: success = PYPI token can yank; auth failure = token is publish-only or wrong project scope
• Delete this workflow after the test is done