- New zfs role with cron-based scrub scheduling for Linux and FreeBSD
- Weekly Sunday scrubs at noon (matching existing manual crons)
- Add zfs_hosts inventory group with london-a and london-b
- Configure zfs_pools per host: zroot (london-a), hdd (london-b)
- Add Prometheus alert rules for degraded/faulted/offline pools
- Add zfs.yml playbook for targeted deploys
Captures the previously untracked scrub cron on london-a and
re-enables the commented-out scrub on london-b.
Refs: PESO-93
