Add proforma invoice step to subscription checkout

Insert a factor/invoice page between plan selection and payment showing
billing-period choice, line items, and totals before redirecting to the
gateway, moving payment-method selection to where the charge happens.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/dashboard/src/app/[locale]/(dashboard)/subscription/checkout/page.tsx

@@ -0,0 +1,10 @@
+import { Suspense } from "react";
+import { CheckoutScreen } from "@/components/subscription/checkout-screen";
+
+export default function SubscriptionCheckoutPage() {
+  return (
+    <Suspense fallback={null}>
+      <CheckoutScreen />
+    </Suspense>
+  );
+}