feat: integrate ErrorService for consistent error display and standardize bloc error messages.

lib/pages/login.dart

@@ -4,6 +4,7 @@ import '../blocs/auth/auth_bloc.dart';
 import '../blocs/auth/auth_event.dart';
 import '../blocs/auth/auth_state.dart';
 import 'package:sign_in_button/sign_in_button.dart';
+import '../services/error_service.dart';
 
 /// Login page widget for user authentication.
 ///
@@ -89,12 +90,7 @@ class _LoginPageState extends State<LoginPage> {
           if (state is AuthAuthenticated) {
             Navigator.pushReplacementNamed(context, '/home');
           } else if (state is AuthError) {
-            ScaffoldMessenger.of(context).showSnackBar(
-              SnackBar(
-                content: Text(state.message),
-                backgroundColor: Colors.red,
-              ),
-            );
+            ErrorService().showError(message: state.message);
           }
         },
         builder: (context, state) {