0.5.1 — deploy-key ceremony comment aligned with the course

gcp-deploy.yaml's one-time-setup comment now mints the github-deployer key into the workspace parent (outside the repo) and has you delete it by hand once gh has stored it — the same ritual as every other robot key — and notes how to extend --update-secrets with additional NAME=NAME:latest pairs. Comment-only change; no behavior differs. (Package version stays 0.0.1 by design.)