vms: add monitoring stack and node-exporter for docker host

utility-101-shadow:
- Add full monitoring stack (Prometheus + Blackbox Exporter + Alertmanager)
  with Docker Compose and a systemd unit (monitoring.service)
- Prometheus scrapes: itself, blackbox-exporter, and node-exporter on
  the docker host (docker:9100); blackbox probes cover HTTPS endpoints
  with TLS cert monitoring
- Alertmanager routes warnings to Slack/Discord, critical alerts also
  to email (Gmail SMTP); inhibit rule suppresses SSLCertExpiringSoon
  when SSLCertExpired already fires
- Alert rules: 11 node-exporter alerts (host down, CPU, memory, disk
  fill/prediction, iowait, OOM kill, systemd failed units) + 3 blackbox
  alerts (probe failed, SSL expiring, SSL expired)
- readme: add services list and Docker Engine installation steps

docker host:
- Add node-exporter container running with host pid/network and
  read-only mounts of /proc, /sys, / for full host metrics visibility
- Enable --collector.systemd for systemd unit state metrics
- Add systemd unit (node-exporter.service) to manage the container

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

vms/utility-101-shadow/readme.md

@@ -1,3 +1,37 @@
+## Services
+
+- wireguard
+- openvpn server
+- dns server (bind)
+
+## Docker
+
+```bash
+# installation
+apt-get install -y ca-certificates curl
+
+# 3. Add Docker's official GPG key
+sudo install -m 0755 -d /etc/apt/keyrings
+sudo curl -fsSL https://download.docker.com/linux/ubuntu/gpg -o /etc/apt/keyrings/docker.asc
+sudo chmod a+r /etc/apt/keyrings/docker.asc
+
+# 4. Add Docker apt repository
+echo \
+  "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/ubuntu \
+  $(. /etc/os-release && echo "$VERSION_CODENAME") stable" | \
+  sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
+
+# 5. Install Docker Engine
+sudo apt-get update
+sudo apt-get install -y docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin
+
+# 6. Enable and start Docker
+sudo systemctl enable docker
+sudo systemctl start docker
+
+
+```
+
 ## named tweaks
 
 1. Generate TSIG key