fix: maintain loading guard during async billing URL fetch

Add await to openAsync call to prevent multiple concurrent requests
when users rapidly click the billing button. This maintains the
loading state until the billing URL is successfully fetched and opened.

Addresses review feedback about regression in loading behavior

web/app/components/billing/pricing/plans/cloud-plan-item/index.tsx

@@ -75,7 +75,7 @@ const CloudPlanItem: FC<CloudPlanItemProps> = ({
     setLoading(true)
     try {
       if (isCurrentPaidPlan) {
-        openAsync(
+        await openAsync(
           () => fetchBillingUrl().then(res => res.url),
           {
             errorMessage: 'Failed to open billing page',