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/i18n/locales/zh.ts

@@ -247,6 +247,8 @@ export default {
     loading: '加载中...',
     justNow: '刚刚',
     save: '保存',
+    saved: '保存成功',
+    deleted: '删除成功',
     cancel: '取消',
     delete: '删除',
     edit: '编辑',
@@ -304,6 +306,7 @@ export default {
     saving: '保存中...',
     selectedCount: '（已选 {count} 个）',
     refresh: '刷新',
+    view: '查看',
     settings: '设置',
     chooseFile: '选择文件',
     notAvailable: '不可用',
@@ -5744,6 +5747,9 @@ export default {
       tabPlanConfig: '套餐配置',
       tabUserSubs: '用户订阅',
       selectGroup: '请选择分组',
+      groupRequired: '请选择订阅分组',
+      priceRequired: '价格必须大于 0',
+      validityDaysRequired: '有效期天数必须大于 0',
       groupMissing: '缺失',
       groupInfo: '分组信息',
       platform: '平台',