fix: force fresh balance data on purchase-options query

Added staleTime: 0 and refetchOnMount: 'always' to purchase-options
queries in SubscriptionPurchase and Subscription pages to prevent
stale balance_kopeks from causing incorrect insufficient funds display.

src/pages/Subscription.tsx

@@ -211,6 +211,8 @@ export default function Subscription() {
   const { data: purchaseOptions } = useQuery({
     queryKey: ['purchase-options'],
     queryFn: subscriptionApi.getPurchaseOptions,
+    staleTime: 0,
+    refetchOnMount: 'always',
   });
 
   const isTariffsMode = purchaseOptions?.sales_mode === 'tariffs';