feat(auth): add countdown timer for resend button

apps/lib/features/auth/ui/screens/register_verification_screen.dart

@@ -1,3 +1,5 @@
+import 'dart:async';
+
 import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:go_router/go_router.dart';
@@ -43,13 +45,38 @@ class RegisterVerificationView extends StatefulWidget {
 
 class _RegisterVerificationViewState extends State<RegisterVerificationView> {
   final _codeController = TextEditingController();
+  Timer? _countdownTimer;
+  int _countdown = 60;
+
+  @override
+  void initState() {
+    super.initState();
+    _startCountdown();
+  }
 
   @override
   void dispose() {
+    _countdownTimer?.cancel();
     _codeController.dispose();
     super.dispose();
   }
 
+  void _startCountdown() {
+    setState(() {
+      _countdown = 60;
+    });
+    _countdownTimer?.cancel();
+    _countdownTimer = Timer.periodic(const Duration(seconds: 1), (timer) {
+      if (_countdown > 0) {
+        setState(() {
+          _countdown--;
+        });
+      } else {
+        timer.cancel();
+      }
+    });
+  }
+
   Future<void> _handleComplete() async {
     final cubit = context.read<RegisterCubit>();
     cubit.verificationCodeChanged(_codeController.text);