fix: handle error message on sign up form

lib/src/providers/auth_provider.dart

@@ -146,12 +146,15 @@ class AuthProvider with ChangeNotifier {
         String token = Token.fromJson(data)!.key;
         storeAccessToken(token);
         isAuthenticated = true;
+        message = null;
 
         if (context.mounted) {
           context.go("/");
         }
         debugPrint("Signup successful $token");
       } else {
+        final data = jsonDecode(response.body);
+        message = data["message"];
         debugPrint(
             "Error: sign up failed, ${response.statusCode}: ${response.body}");
       }

lib/src/widgets/forms/sign_up_form.dart

@@ -40,6 +40,8 @@ class _SignUpForm extends State<SignUpForm> {
     const String formText = "Sign In to get started";
 
     return Consumer<AuthProvider>(builder: (context, authProvider, child) {
+      final message = authProvider.message;
+
       return Column(
         children: [
           Padding(
@@ -120,8 +122,10 @@ class _SignUpForm extends State<SignUpForm> {
                     },
                     keyboardType: TextInputType.visiblePassword,
                   ),
-                  const SizedBox(
-                    height: 20.0,
+                  Padding(
+                    padding: const EdgeInsets.symmetric(vertical: 20.0),
+                    child: Text(message ?? "",
+                        style: const TextStyle(color: Colors.red)),
                   ),
                   Column(
                     children: [