prometheus.yml was missing the rule_files section, so alerting rules
deployed to /usr/local/etc/prometheus/rules/ were never loaded.
- Add rule_files glob so Prometheus evaluates the ZFS pool rules
- Document that alerting notifications go through Grafana, not
Alertmanager — no alerting: section needed
- Remove node-exporter.rules (all rules were commented out)
Resolves PESO-103
- 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
