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/en.json

@@ -2059,7 +2059,10 @@
         "startDate": "Start Date",
         "endDate": "End Date",
         "total": "{count} records total",
+        "totalRecords": "Total Records",
         "maxRecords": "Max {count} records",
+        "maxRecordsLabel": "Max Records",
+        "unlimited": "Unlimited",
         "notStreamType": "This variable is not a record type",
         "deleteRecord": "Delete Record",
         "deleteConfirm": "Are you sure you want to delete this record?",