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

frontend/app/lib/auth/feedback.dart

@@ -23,6 +23,9 @@ class AuthFeedback extends StatelessWidget {
             AuthError.emailInUse => l.authEmailInUse,
             AuthError.unavailable => l.authUnavailable,
             AuthError.unexpected => l.authUnexpected,
+            AuthError.factorLocked => l.factorLocked,
+            AuthError.factorCooldown => l.factorWait,
+            AuthError.factorRequired => l.factorRequired,
           };
     return Semantics(
       liveRegion: true,