ops: align vps desired state with control-plane architecture, remove legacy agent-system references

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

hosts/vps/services.txt

@@ -1 +0,0 @@
-npm

hosts/vps/services.yaml

@@ -23,7 +23,7 @@ services:
       local:
         - stability-agent
       external:
-        - piha:agent-system-redis
+        - piha:redis
     ports:
       - name: http
         container_port: 18180
@@ -32,3 +32,12 @@ services:
       config_path: /opt/homelab/config/control-plane
       data_path: /opt/homelab/data/control-plane
       logs_path: /opt/homelab/logs/control-plane
+
+  node_exporter:
+    role: metrics-exporter
+    deployment_model: docker-compose
+    exposure: local-only
+    offline_required: true
+    depends_on:
+      local: []
+      external: []

inventory/topology.yaml

@@ -27,6 +27,7 @@ nodes:
     roles:
       - edge
       - ingress
+      - control-plane
 
   chelsty-infra:
     site: chelsty