feat(routing): Lab Host Router closes the Gateway-to-Lab cross-VM gap

Adds platform/lab-router/ — a narrow service that runs on the Lab Host,
authenticates the Gateway via mTLS, and resolves an opaque routing token to
a local container purely from Docker label state (no Postgres access, no
callback to the Provisioner). Replaces the Gateway's env.internal_ip
assumption (only valid when Gateway and Lab share a Docker daemon) with a
data-driven direct/router decision per lab_host
(lab_hosts.routing_mode/router_endpoint, migration 004), resolved in one
place (platform/gateway/src/lab-endpoint.js's labTarget()) that every
proxy/fetch call site in server.js now goes through.

Extends the existing Docker TLS CA (infra/scripts/docker-tls/generate-docker-tls.sh)
with a second mTLS leaf pair (router-server/gateway-client) for this new
data-plane connection, deployed by the docker-tls Ansible role into a
separate directory from the control-plane pair. Firewall
(rn-lab-host-01.rules) replaces the old speculative wide port-range
allowance with one narrow rule: platform_ip -> the Router's port only.

dev-local stays routing_mode: direct — zero behavior change for local dev,
confirmed by the full existing regression suite passing unmodified.

infra/scripts/ci/tag-and-push.sh

@@ -22,6 +22,7 @@ declare -A IMAGES=(
   [rootnode/gateway]="platform/gateway/Dockerfile platform/gateway"
   [rootnode/provisioner]="platform/provisioner/Dockerfile platform/provisioner"
   [rootnode/egress-proxy]="platform/egress-proxy/Dockerfile platform/egress-proxy"
+  [rootnode/lab-router]="platform/lab-router/Dockerfile platform/lab-router"
   [rootnode/lab]="Dockerfile ."
 )