more robust nginx configuration, notably for "certbot --nginx -d DOMAIN";

--- a/src/Pure/Tools/phabricator.scala	Tue Jan 23 12:28:35 2024 +0100
+++ b/src/Pure/Tools/phabricator.scala	Tue Jan 23 15:02:52 2024 +0100
@@ -88,6 +88,9 @@
     override def site_init(name: String, server_name: String, webroot: String): Unit = {
       File.write(site_conf(name),
 """server {
+  listen 80;
+  listen [::]:80;
+
   server_name """ + server_name + """;
   root """ + webroot + """;