ghostty: validate configuration on change

Runs `ghostty +validate-config` when the configuration file changes.

Co-authored-by: Heitor Augusto <IAm.HeitorALN@proton.me>

modules/programs/ghostty.nix

@@ -120,6 +120,7 @@ in {
         {
           "ghostty/config" = lib.mkIf (cfg.settings != { }) {
             source = keyValue.generate "ghostty-config" cfg.settings;
+            onChange = "${lib.getExe cfg.package} +validate-config";
           };
         }