Navigation now flows entirely through go_router

frontend/pweb/lib/pages/payment_methods/widgets/state_view.dart

@@ -0,0 +1,21 @@
+import 'package:flutter/material.dart';
+
+class PaymentMethodsLoadingView extends StatelessWidget {
+  const PaymentMethodsLoadingView({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return const Center(child: CircularProgressIndicator());
+  }
+}
+
+class PaymentMethodsErrorView extends StatelessWidget {
+  final String message;
+
+  const PaymentMethodsErrorView({super.key, required this.message});
+
+  @override
+  Widget build(BuildContext context) {
+    return Center(child: Text(message));
+  }
+}