refactor: improve cloud variable records page with standard DataTable layout

- Add statistics cards (total records, variable key, max records, scope)
- Use standard DataTable component with toolbar template
- Add BulkActions component for batch operations
- Add DataTableViewOptions for column visibility control
- Dynamic columns are generated from record data fields
- Add missing i18n keys (totalRecords, maxRecordsLabel, unlimited)
- Match styling with other admin data table pages

frontend/src/plugins/i18n/zh.json

@@ -2048,7 +2048,10 @@
         "startDate": "开始日期",
         "endDate": "结束日期",
         "total": "共 {count} 条记录",
+        "totalRecords": "总记录数",
         "maxRecords": "最大 {count} 条",
+        "maxRecordsLabel": "最大记录数",
+        "unlimited": "不限制",
         "notStreamType": "该变量不是记录类型",
         "deleteRecord": "删除记录",
         "deleteConfirm": "确定要删除该条记录吗？",