phosh: Enable xwayland support

This fixes an issue where some applications would fail to open entirely
at the cost of lower quality graphics.

modules/desktop.nix

@@ -82,6 +82,10 @@ in
           enable = true;
           group = "users";
           user = username;
+
+          phocConfig = {
+            xwayland = "immediate";
+          };
         };
       };