Add dufs user to users group

shared/modules/services/dufs.nix

@@ -133,6 +133,7 @@ in
     users.users.${cfg.user} = {
       isSystemUser = true;
       group = cfg.group;
+      extraGroups = [ "users" ];  # Add to users group for access to shared files
       description = "dufs file server user";
     };