feat(security): production Compose topology, firewall rulesets, Docker mTLS

Named-bridge-network production Compose (not host networking, unlike dev)
for rn-platform-01; egress-proxy + agents for rn-lab-host-01. Caddy reverse
proxy, single public origin, Grafana restricted to management_cidr.
iptables-restore firewall rulesets for all three hosts (Proxmox host,
rn-platform-01, rn-lab-host-01) codifying the Platform/Lab-Host boundary:
no student-to-student traffic, no direct Proxmox exposure, no direct
Postgres/Provisioner exposure from the Lab Host.

Mutual TLS for the Provisioner<->Lab Host Docker connection: certificate
generation/verification scripts, dockerd TLS config, firewall-restricted
port 2376. Application support already existed since Phase 1; this is
purely the operational half.

Validated: docker compose config, caddy validate, firewall structural lint,
and a real openssl s_server/s_client mTLS handshake proving the cert chain
and mutual-auth rejection (legitimate client verified, rogue client
correctly rejected with verify code 19).

infra/docker/lab-host/docker-compose.production.yml

@@ -0,0 +1,68 @@
+# Production compose for rn-lab-host-01. Deployed by infra/ansible/roles/lab-host/ to
+# /opt/rootnode/lab-host/docker-compose.yml, run as a systemd unit
+# (rootnode-lab-host.service.j2). Runs exactly one long-lived service: the shared egress proxy
+# every student Lab's outbound traffic passes through (platform/egress-proxy/, unchanged since
+# Phase 1). Student Lab containers themselves are NOT part of this compose file — they're
+# created/destroyed individually by the Provisioner over the remote Docker TLS endpoint
+# (dockerd itself, not compose), same mechanism as dev, just remote.
+
+networks:
+  rn-egress:
+    driver: bridge
+
+services:
+  egress-proxy:
+    image: "{{ registry }}/rootnode/egress-proxy:{{ image_tag }}"
+    restart: unless-stopped
+    ports:
+      - "3128:3128"   # reachable from every per-Lab Docker network on this host — restricted
+                       # to those networks by the Provisioner's per-environment DOCKER-USER
+                       # chains, not by a published-port firewall rule (there is no sensible
+                       # single source IP to restrict this to; the egress proxy's OWN allowlist
+                       # is the actual control, see platform/egress-proxy/allowlist.txt)
+    networks: [rn-egress]
+
+  node-exporter:
+    image: prom/node-exporter:latest
+    restart: unless-stopped
+    network_mode: host
+    pid: host
+    volumes:
+      - /proc:/host/proc:ro
+      - /sys:/host/sys:ro
+      - /:/rootfs:ro
+    command:
+      - "--path.procfs=/host/proc"
+      - "--path.sysfs=/host/sys"
+      - "--path.rootfs=/rootfs"
+      - "--collector.filesystem.mount-points-exclude=^/(sys|proc|dev|host|etc)($$|/)"
+
+  cadvisor:
+    image: gcr.io/cadvisor/cadvisor:latest
+    restart: unless-stopped
+    privileged: true
+    devices:
+      - /dev/kmsg
+    volumes:
+      - /:/rootfs:ro
+      - /var/run:/var/run:ro
+      - /sys:/sys:ro
+      - /var/lib/docker/:/var/lib/docker:ro
+    ports:
+      - "8080:8080"   # scraped remotely by Prometheus on rn-platform-01 — restricted to that
+                       # one source IP by the host firewall (rn-lab-host-01.rules), not by
+                       # binding to localhost, since Prometheus isn't local on this host.
+
+  promtail:
+    image: grafana/promtail:latest
+    restart: unless-stopped
+    volumes:
+      - /opt/rootnode/lab-host/promtail-config.yml:/etc/promtail/config.yml:ro
+      - /var/run/docker.sock:/var/run/docker.sock:ro
+      - /var/log/journal:/var/log/journal:ro
+      - /etc/machine-id:/etc/machine-id:ro
+    command: ["-config.file=/etc/promtail/config.yml"]
+    # host networking so promtail can reach Loki on rn-platform-01 over the network — this
+    # traffic is OUTBOUND from rn-lab-host-01 (log push, client-initiated), which the host
+    # firewall's default-ACCEPT OUTPUT chain already allows; nothing new needed there.
+    network_mode: host