feat(payment): refactor payment configuration retrieval into a custom hook

assets/admin/hooks/usePaymentConfig.ts

@@ -0,0 +1,12 @@
+import { useQuery } from '@tanstack/react-query';
+import { api } from '../lib/api';
+import type { ApiResponse } from '../lib/api';
+
+export function usePaymentConfig() {
+  const { data } = useQuery<ApiResponse<{ test_mode: boolean }>>({
+    queryKey: ['payment-config'],
+    queryFn: () => api.get('/api/v1/payment/config'),
+    staleTime: 5 * 60 * 1000,
+  });
+  return { isTestMode: data?.data?.test_mode ?? false };
+}