fixup! TF-4224 Reduce ReDoS vulnerability

lib/main/utils/app_utils.dart

@@ -14,6 +14,10 @@ import 'package:tmail_ui_user/main/universal_import/html_stub.dart' as html;
 class AppUtils {
   const AppUtils._();
 
+  static final _emailLocalhostRegex = RegExp(
+    r'^(?:"[^"\r\n]+"|[^<>()[\]\\.,;:\s@"]+(?:\.[^<>()[\]\\.,;:\s@"]+)*)@localhost$',
+  );
+
   static Future<void> loadEnvFile() async {
     await dotenv.load(fileName: AppConfig.envFileName);
     final mapEnvData = Map<String, String>.from(dotenv.env);
@@ -53,9 +57,7 @@ class AppUtils {
 
   static bool isEmailLocalhost(String email) {
     final normalized = email.trim();
-    return RegExp(
-        r'^(?:"[^"\r\n]+"|[^<>()[\]\\.,;:\s@"]+(?:\.[^<>()[\]\\.,;:\s@"]+)*)@localhost$'
-    ).hasMatch(normalized);
+    return _emailLocalhostRegex.hasMatch(normalized);
   }
 
   static void copyEmailAddressToClipboard(BuildContext context, String emailAddress) {