The promote workflow previously pulled :latest, which could be stale if the
staging build hadn't finished yet. Now it pulls the exact :SHA image that
deploy.yml produces, with retry logic (up to 10min) if staging is still building.
- Push to main builds ARM64 image and deploys to docfast-staging namespace
- Push a version tag (v*) promotes latest image to docfast namespace (prod)
- Both use same deployer SA with namespace-scoped RBAC