feat: enhance routing logic and improve login screen validation; add guarded API call for error handling

flutter/lib/core/api/guarded_api_call.dart

@@ -0,0 +1,18 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import 'api_exception.dart';
+import '../../features/auth/data/auth_providers.dart';
+
+/// Executes [call] and automatically logs out the user if the server
+/// returns 401 Unauthorized. Re-throws the exception so the calling
+/// widget/provider can still display an error if needed.
+Future<T> guardedApiCall<T>(Ref ref, Future<T> Function() call) async {
+  try {
+    return await call();
+  } on ApiException catch (e) {
+    if (e.type == ApiErrorType.unauthorized) {
+      await ref.read(authStateProvider.notifier).logout();
+    }
+    rethrow;
+  }
+}