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/data/models/auth_models_test.dart

@@ -4,33 +4,32 @@ import 'package:social_app/features/auth/data/models/login_request.dart';
 import 'package:social_app/features/auth/data/models/auth_response.dart';
 
 void main() {
-  group('SignupStartRequest', () {
-    test('serializes to JSON', () {
-      final request = SignupStartRequest(
-        username: 'testuser',
-        email: 'test@example.com',
-        password: 'password123',
-      );
+  group('OtpSendRequest', () {
+    test('serializes e164 phone to JSON', () {
+      final request = OtpSendRequest(phone: '+14155552671');
 
       final json = request.toJson();
 
-      expect(json['username'], 'testuser');
-      expect(json['email'], 'test@example.com');
-      expect(json['password'], 'password123');
+      expect(json['phone'], '+14155552671');
+    });
+
+    test('normalizes 00 prefix to plus', () {
+      final request = OtpSendRequest(phone: '0014155552671');
+
+      final json = request.toJson();
+
+      expect(json['phone'], '+14155552671');
     });
   });
 
   group('LoginRequest', () {
-    test('serializes to JSON', () {
-      final request = LoginRequest(
-        email: 'test@example.com',
-        password: 'password123',
-      );
+    test('serializes e164 to JSON', () {
+      final request = LoginRequest(phone: '+14155552671', token: '123456');
 
       final json = request.toJson();
 
-      expect(json['email'], 'test@example.com');
-      expect(json['password'], 'password123');
+      expect(json['phone'], '+14155552671');
+      expect(json['token'], '123456');
     });
   });
 
@@ -41,7 +40,7 @@ void main() {
         'refresh_token': 'test_refresh',
         'expires_in': 3600,
         'token_type': 'bearer',
-        'user': {'id': '123', 'email': 'test@example.com'},
+        'user': {'id': '123', 'phone': '+8613812345678'},
       };
 
       final response = AuthResponse.fromJson(json);
@@ -50,7 +49,7 @@ void main() {
       expect(response.refreshToken, 'test_refresh');
       expect(response.expiresIn, 3600);
       expect(response.user.id, '123');
-      expect(response.user.email, 'test@example.com');
+      expect(response.user.phone, '+8613812345678');
     });
   });
 }