fix(auth): correct resend response type and improve error messages

apps/lib/features/auth/data/auth_api.dart

@@ -25,12 +25,12 @@ class AuthApi {
     return AuthResponse.fromJson(response.data);
   }
 
-  Future<SignupStartResponse> signupResend(SignupResendRequest request) async {
+  Future<SignupResendResponse> signupResend(SignupResendRequest request) async {
     final response = await _client.post(
       '$_prefix/signup/resend',
       data: request.toJson(),
     );
-    return SignupStartResponse.fromJson(response.data);
+    return SignupResendResponse.fromJson(response.data);
   }
 
   Future<AuthResponse> login(LoginRequest request) async {

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

@@ -5,7 +5,7 @@ import 'package:social_app/features/auth/data/models/auth_response.dart';
 abstract class AuthRepository {
   Future<SignupStartResponse> signupStart(SignupStartRequest request);
   Future<AuthResponse> signupVerify(SignupVerifyRequest request);
-  Future<SignupStartResponse> signupResend(SignupResendRequest request);
+  Future<SignupResendResponse> signupResend(SignupResendRequest request);
   Future<AuthResponse> login(LoginRequest request);
   Future<AuthResponse> refresh(String refreshToken);
   Future<void> logout();

apps/lib/features/auth/data/auth_repository_impl.dart

@@ -29,7 +29,7 @@ class AuthRepositoryImpl implements AuthRepository {
   }
 
   @override
-  Future<SignupStartResponse> signupResend(SignupResendRequest request) {
+  Future<SignupResendResponse> signupResend(SignupResendRequest request) {
     return _api.signupResend(request);
   }
 

apps/lib/features/auth/data/models/auth_response.dart

@@ -54,3 +54,13 @@ class SignupStartResponse {
     );
   }
 }
+
+class SignupResendResponse {
+  final String message;
+
+  const SignupResendResponse({required this.message});
+
+  factory SignupResendResponse.fromJson(Map<String, dynamic> json) {
+    return SignupResendResponse(message: json['message'] as String);
+  }
+}