Add Proxmox firewall configs and Grafana dashboards

- proxmox/firewall/host.fw: host firewall rules (SSH/Proxmox UI/SPICE
  from LAN, DNS from internal subnets, ICMP)
- proxmox/firewall/cluster.fw: cluster firewall with network aliases
- files/grafana-dashboards/node-exporter-full.json: Node Exporter Full
  (grafana.com/dashboards/1860)
- files/grafana-dashboards/loki-logs.json: Logs/App dashboard for Loki
  (grafana.com/dashboards/13639)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

proxmox/firewall/cluster.fw

@@ -0,0 +1,7 @@
+[OPTIONS]
+enable: 1
+
+[ALIASES]
+lan 192.168.1.0/24
+infra_net 10.10.1.0/24
+dev_net 10.10.2.0/24

proxmox/firewall/host.fw

@@ -0,0 +1,12 @@
+[OPTIONS]
+enable: 1
+log_level_in: nolog
+log_level_out: nolog
+
+[RULES]
+IN ACCEPT -source 192.168.1.0/24 -p tcp -dport 22
+IN ACCEPT -source 192.168.1.0/24 -p tcp -dport 8006
+IN ACCEPT -source 192.168.1.0/24 -p tcp -dport 3128
+IN ACCEPT -source 10.10.0.0/16 -p udp -dport 53
+IN ACCEPT -source 10.10.0.0/16 -p tcp -dport 53
+IN ACCEPT -p icmp