/usr/local/bin/cayce-check-backup-freshness (from
deploy/backup/check-freshness.sh): exits 1 if the newest
/var/backups/cayce/YYYY-MM-DD/ dir has mtime older than 26h, or if no
backups exist while the age recipient IS configured (backups expected).
Info-exit-0 when backups have never been configured. Not attached to a
timer (only cayce-backup.timer was authorized); documented for manual
or cron use.
Verified: fresh dir => OK 0h exit 0; dir with 2-day mtime => ALERT 48h
exit 1; no-dir + recipient => ALERT; no-dir + no-recipient => INFO.
