feat: implement social login functionality with Google, Facebook, and Twitter, including API integration and platform-specific configurations.

lib/features/auth/data/auth_repository.dart

@@ -130,6 +130,44 @@ class AuthRepository {
     }
   }
 
+  /// Social auth (Google, Facebook, etc.) — calls POST /auth/social
+  Future<UserModel> socialAuth({
+    required String provider,
+    required String providerId,
+    required String email,
+    String? name,
+    String? avatar,
+  }) async {
+    try {
+      final response = await _dio.post(
+        ApiConstants.authSocial,
+        data: {
+          'provider': provider,
+          'providerId': providerId,
+          'email': email,
+          if (name != null) 'name': name,
+          if (avatar != null) 'avatar': avatar,
+        },
+      );
+
+      final data = response.data['data'] as Map<String, dynamic>;
+      final authResponse = AuthResponse.fromJson(data);
+
+      await SecureStorage.saveTokens(
+        accessToken: authResponse.accessToken,
+        refreshToken: authResponse.refreshToken,
+      );
+
+      return authResponse.user;
+    } on DioException catch (e) {
+      if (e.error is ApiException) throw e.error as ApiException;
+      throw ApiException(
+        message: e.message ?? 'Social login failed',
+        statusCode: e.response?.statusCode,
+      );
+    }
+  }
+
   /// Register returns { message, user } — no tokens.
   /// The user must verify their email before logging in.
   Future<Map<String, dynamic>> register(RegisterRequest request) async {