tuned: more standard;

--- a/src/Pure/Build/build_manager.scala	Sat Feb 01 19:29:54 2025 +0100
+++ b/src/Pure/Build/build_manager.scala	Sat Feb 01 20:46:01 2025 +0100
@@ -1721,7 +1721,7 @@
       val dirs = new mutable.ListBuffer[Path]
       val build_hosts = new mutable.ListBuffer[Build_Cluster.Host]
       var options = Options.init()
-      var port = 8080
+      var port = 0
 
       val getopts = Getopts("""
 Usage: isabelle build_manager [OPTIONS]