chore: initial import from KNEL/PFVCluster@041d311 [#769]

Split per O&M lane work order. Full history: KNEL/PFVCluster.
https://projects.knownelement.com/issues/769#note-4152

dhcp/install-dhcp.sh

@@ -0,0 +1,31 @@
+#!/bin/bash
+# install-dhcp.sh — installs isc-dhcp-server + Webmin on a netinfra node.
+# Does NOT start the DHCP service. Run on the target node itself.
+set -e
+
+echo "=== Installing isc-dhcp-server ==="
+apt-get update -qq
+apt-get install -y isc-dhcp-server
+
+echo "=== Installing Webmin ==="
+if ! dpkg -l | grep -q '^ii.*webmin'; then
+  curl -fsSL https://raw.githubusercontent.com/webmin/webmin/master/webmin-setup-repo.sh -o /tmp/webmin-setup.sh
+  sh /tmp/webmin-setup.sh -f
+  rm -f /tmp/webmin-setup.sh
+  apt-get install -y webmin
+else
+  echo "Webmin already installed"
+fi
+
+echo "=== Writing /etc/default/isc-dhcp-server ==="
+cat > /etc/default/isc-dhcp-server <<'EOF'
+# Defaults for isc-dhcp-server (sourced by /etc/init.d/isc-dhcp-server)
+INTERFACESv4="ens18"
+INTERFACESv6=""
+EOF
+
+echo "=== Stopping DHCP service (should not serve yet) ==="
+systemctl stop isc-dhcp-server 2>/dev/null || true
+systemctl disable isc-dhcp-server 2>/dev/null || true
+
+echo "=== Done. DHCP installed but NOT started. ==="