Add reusable two-factor verification for login and money operations (#32)

frontend/app/test/localization_test.dart

@@ -60,7 +60,13 @@ void main() {
     final ru = jsonDecode(File('lib/l10n/ru.arb').readAsStringSync()) as Map;
     expect(ru.keys.toSet(), en.keys.toSet());
     expect(
-      ru.values.every((value) => value is String && value.trim().isNotEmpty),
+      ru.entries
+          .where((entry) => !entry.key.toString().startsWith('@'))
+          .every(
+            (entry) =>
+                entry.value is String &&
+                (entry.value as String).trim().isNotEmpty,
+          ),
       isTrue,
     );
   });