feat: comprehensive observability stack

- Add restic_backups and mattermost scrape jobs to Prometheus config
- Add UnPoller deployment+service+secret for UniFi metrics (unpoller.yaml)
- Add unifi scrape job targeting unpoller in-cluster
- Add 4 Grafana dashboards as NixOS-managed etc files on hosea:
  - system-health: CPU, memory, disk, network per host
  - backup-health: restic backup freshness and duration
  - kubernetes: pod counts, restart rates, node resources
  - network: DNS queries, DHCP leases, UniFi ports, ping latency
- Add grafana-api-token agenix secret placeholder on hosea
- Open firewall ports 9100/9427/9558 for prometheus exporters in baseline.nix

manifests/monitoring/config.yaml

@@ -56,6 +56,22 @@ data:
         static_configs:
           - targets:
               - "hosea.shire-zebra.ts.net:9108"
+      # Restic rest-server backup metrics
+      - job_name: restic_backups
+        static_configs:
+          - targets:
+              - "nas1.shire-zebra.ts.net:30248"
+      # Mattermost metrics
+      - job_name: mattermost
+        metrics_path: /metrics
+        static_configs:
+          - targets:
+              - "mattermost.thehellings.lan:8065"
+      # UniFi metrics via unpoller
+      - job_name: unifi
+        static_configs:
+          - targets:
+              - "unpoller.monitoring.svc.cluster.local:9130"
       # This scrapes metrics from the Kubernetes kubelets
       - job_name: kubelet
         kubernetes_sd_configs: