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/lib/features/auth/data/auth_repository.dart

@@ -1,24 +1,15 @@
-import 'package:social_app/features/auth/data/models/signup_request.dart';
-import 'package:social_app/features/auth/data/models/login_request.dart';
 import 'package:social_app/features/auth/data/models/auth_response.dart';
 
 abstract class AuthRepository {
-  Future<VerificationCreateResponse> createVerification(
-    SignupStartRequest request,
-  );
-  Future<AuthResponse> verifyVerification(SignupVerifyRequest request);
-  Future<void> resendVerification(SignupResendRequest request);
-  Future<AuthResponse> createSession(LoginRequest request);
+  Future<void> sendOtp(String phone);
+  Future<AuthResponse> createPhoneSession({
+    required String phone,
+    required String token,
+  });
   Future<AuthResponse> refreshSession(String refreshToken);
   Future<void> deleteSession();
   Future<void> clearSessionLocalOnly();
   Future<String?> getAccessToken();
   Future<String?> getRefreshToken();
   Future<bool> isAuthenticated();
-  Future<void> requestPasswordReset(String email);
-  Future<void> confirmPasswordReset({
-    required String email,
-    required String token,
-    required String newPassword,
-  });
 }