New tasks: db-backup, maintenance-on/off, health-check, prune-releases,
list-releases.
New story: releases.
Updated tasks: restart-service (fail-fast), harden-release (skip vendor),
clone-release (--depth=1), rollback-release (validate target).
init story now correctly skips db-backup/maintenance/prune.
deploy story includes maintenance window with operator-printable secret.

Stub: stubs/config/backup_predeploy.php with namespaced retention.
Wired into 'app-config' component configs.