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/composables/useTableSelection.ts

@@ -76,6 +76,12 @@ export function useTableSelection<T>({ rows, getId }: UseTableSelectionOptions<T
     replaceSelectedSet(next)
   }
 
+  const batchUpdate = (updater: (draft: Set<number>) => void) => {
+    const draft = new Set(selectedSet.value)
+    updater(draft)
+    replaceSelectedSet(draft)
+  }
+
   const selectVisible = () => {
     toggleVisible(true)
   }
@@ -93,6 +99,7 @@ export function useTableSelection<T>({ rows, getId }: UseTableSelectionOptions<T
     clear,
     removeMany,
     toggleVisible,
-    selectVisible
+    selectVisible,
+    batchUpdate
   }
 }