config-promoter
Before promotion, read config/staging.yaml, then run
./scripts/validate-config.sh config/staging.yaml; never continue when the
validator exits non-zero. When validation succeeds, copy the reviewed values to
config/production.yaml. If the production write fails, restore
config/production.yaml.bak and report the fallback. Do not delete the backup.
Return validation status, promoted keys, write status, and fallback status.