fix(private-room): preserve payment return route

src/app/subscription/components/subscription-checkout-button.tsx

@@ -6,6 +6,7 @@
  */
 import { usePaymentLaunchFlow } from "@/app/_hooks/use-payment-launch-flow";
 import { PaymentLaunchDialogs } from "@/app/_components/payment/payment-launch-dialogs";
+import type { SubscriptionReturnTo } from "@/lib/navigation/subscription_exit";
 import {
   usePaymentDispatch,
   usePaymentState,
@@ -20,7 +21,7 @@ export interface SubscriptionCheckoutButtonProps {
   /** 是否可用（未选套餐 / 未勾选协议 → false） */
   disabled?: boolean;
   subscriptionType: "vip" | "topup";
-  returnTo?: "chat" | null;
+  returnTo?: SubscriptionReturnTo;
 }
 
 export function SubscriptionCheckoutButton({