ops(cloud-run): make candidate rollout and cutover fail-safe

[git-ksk]

Summary

• add a guarded Cloud Run rollout command for inspect / prepare / cutover / rollback
• require immutable image digests and reconcile only proven stale desired traffic
• gate zero-traffic candidates on Ready/ContainerHealthy, production resource bounds, zero startup ERROR logs, and public-origin preflight
• preserve the prior healthy revision until explicit post-Human-acceptance cutover

Validation

• npm run check: 366 tests, 361 pass / 0 fail / 5 platform skips
• npm run build
• git diff --check

Refs #170