fix: restore DNS during invalid-device uninstall

cmd/cli/main.go

@@ -64,6 +64,9 @@ const (
 	cdOrgFlagName          = "cd-org"
 	customHostnameFlagName = "custom-hostname"
 	nextdnsFlagName        = "nextdns"
+
+	// autoIface is the sentinel --iface value meaning "use the default gateway interface".
+	autoIface = "auto"
 )
 
 // init initializes the default logger before any CLI commands are executed