fix: merge general improvements from release branch

Backend:
- gateway_handler: pass subject.UserID instead of int64(0) for user-level routing
- setting_handler: add missing BalanceLowNotifyRechargeURL to UpdateSettings response
- openai_gateway_service: use applyAccountStatsCost for account stats pricing integration
- embed_on: add local file override (data/public/) for embedded frontend assets

Frontend:
- useTableSelection: add batchUpdate method for batch operations
- AccountsView: virtual scrolling params, Set-based isSelected, swipe virtualization
- ProxiesView: add batchUpdate to selection and swipe-select
- BulkEditAccountModal: fix submit handler to prevent event object as argument
- SettingsView: move payload construction outside try block
- i18n: add general translation keys (saved, deleted, view, validation, allowUserRefund)
- api/client: reorder error fields for consistency
- stores/payment: clarify pollOrderStatus JSDoc

frontend/src/stores/payment.ts

@@ -66,7 +66,7 @@ export const usePaymentStore = defineStore('payment', () => {
     return response.data
   }
 
-  /** Poll order status by ID */
+  /** Poll order status by ID (read-only, no upstream check) */
   async function pollOrderStatus(orderId: number): Promise<PaymentOrder | null> {
     try {
       const response = await paymentAPI.getOrder(orderId)