Monitors without a parentRef are placed under the root group set by
KUMA_ROOT_GROUP (kuma-sync/renner-uno). Only the root references the
email notification, so a fleet-wide outage sends one DOWN and one UP mail
listing the affected groups. resendInterval (consecutive DOWN heartbeats)
is now a managed KumaMonitor field; the root resends hourly while down.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>