Prod runs Python 3.13.7, not the originally planned 3.12. Align the
stack: CI both jobs 3.12->3.13, the IIS install runbook and the dev
setup guide to 3.13 (winget Python.Python.3.13). NOTE for whoever
maintains the offline kit: its wheels are still cp312 and must be
regenerated as cp313 before the next air-gapped deploy.