feat(auth): transition from email to phone-based OTP authentication

- Replace Email+Password login with Phone+OTP flow
- Remove RegisterCubit and registration screens (email verification)
- Remove ResetPasswordCubit and reset password screens
- Add phone normalization and international dial code support
- Update LoginCubit with sendCode/resend cooldown logic
- Add new widgets: phone prefix selector, confirm sheet
- Update all auth API endpoints: /otp/send, /phone-session
- Update form inputs: Email -> Phone with E.164 validation
- Update tests for new auth flow

apps/test/features/auth/presentation/cubits/login_cubit_test.dart

@@ -1,4 +1,5 @@
 import 'package:bloc_test/bloc_test.dart';
+import 'package:fake_async/fake_async.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:formz/formz.dart';
 import 'package:mocktail/mocktail.dart';
@@ -26,17 +27,68 @@ void main() {
     });
 
     blocTest<LoginCubit, LoginState>(
-      'emailChanged updates email',
+      'phoneChanged updates phone',
       build: () => cubit,
-      act: (c) => c.emailChanged('test@example.com'),
+      act: (c) => c.phoneChanged('+8613812345678'),
       expect: () => [isA<LoginState>()],
     );
 
     blocTest<LoginCubit, LoginState>(
-      'passwordChanged updates password',
+      'codeChanged updates code',
       build: () => cubit,
-      act: (c) => c.passwordChanged('password123'),
+      act: (c) => c.codeChanged('123456'),
       expect: () => [isA<LoginState>()],
     );
+
+    test('sendCode success starts 60s cooldown', () {
+      when(() => mockRepository.sendOtp(any())).thenAnswer((_) async {});
+
+      fakeAsync((async) {
+        cubit.phoneChanged('13812345678');
+
+        cubit.sendCode();
+        async.flushMicrotasks();
+
+        expect(cubit.state.resendCooldownSeconds, 60);
+
+        async.elapse(const Duration(seconds: 1));
+        expect(cubit.state.resendCooldownSeconds, 59);
+
+        async.elapse(const Duration(seconds: 59));
+        expect(cubit.state.resendCooldownSeconds, 0);
+      });
+    });
+
+    test('sendCode is blocked during cooldown', () async {
+      when(() => mockRepository.sendOtp(any())).thenAnswer((_) async {});
+      cubit.phoneChanged('13812345678');
+
+      final first = await cubit.sendCode();
+      final second = await cubit.sendCode();
+
+      expect(first, isTrue);
+      expect(second, isFalse);
+      verify(() => mockRepository.sendOtp(any())).called(1);
+    });
+
+    test('phone change resets cooldown and code state', () {
+      when(() => mockRepository.sendOtp(any())).thenAnswer((_) async {});
+
+      fakeAsync((async) {
+        cubit.phoneChanged('13812345678');
+        cubit.codeChanged('123456');
+        cubit.sendCode();
+        async.flushMicrotasks();
+
+        expect(cubit.state.resendCooldownSeconds, 60);
+        expect(cubit.state.codeSent, isTrue);
+
+        cubit.phoneChanged('14155552671');
+
+        expect(cubit.state.resendCooldownSeconds, 0);
+        expect(cubit.state.codeSent, isFalse);
+        expect(cubit.state.code.value, '');
+      });
+    });
   });
 }