fix: format Documents column with user locale in OpenSearch admin

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/pages/Admin/OpenSearchAdminPage.tsx

@@ -13,7 +13,7 @@ export default function OpenSearchAdminPage() {
   const indexColumns: Column<any>[] = [
     { key: 'name', header: 'Index' },
     { key: 'health', header: 'Health', render: (v) => <Badge label={String(v)} color={v === 'green' ? 'success' : v === 'yellow' ? 'warning' : 'error'} /> },
-    { key: 'docCount', header: 'Documents', sortable: true },
+    { key: 'docCount', header: 'Documents', sortable: true, render: (v) => Number(v).toLocaleString() },
     { key: 'size', header: 'Size' },
     { key: 'primaryShards', header: 'Shards' },
   ];