Fall back to IP or MAC in DisplayName when no names available

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

types.go

@@ -239,9 +239,7 @@ func (n *Node) String() string {
 }
 
 func (n *Node) DisplayName() string {
-	if len(n.Names) == 0 {
+	if len(n.Names) > 0 {
-		return ""
-	}
 		var names []string
 		for name := range n.Names {
 			names = append(names, name)
@@ -249,6 +247,18 @@ func (n *Node) DisplayName() string {
 		sortNamesByLength(names)
 		return strings.Join(names, "/")
 	}
+	for _, iface := range n.Interfaces {
+		for ip := range iface.IPs {
+			return ip
+		}
+	}
+	for _, iface := range n.Interfaces {
+		if iface.MAC != "" {
+			return string(iface.MAC)
+		}
+	}
+	return ""
+}
 
 func (n *Node) FirstMAC() string {
 	for _, iface := range n.Interfaces {