feat(mui): migrate Warehouse overview + replace residual admin-loading loaders with LoadingState

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/admin/pages/Users.tsx

@@ -25,6 +25,7 @@ import {
   SwitchField,
   Select,
   StatusChip,
+  LoadingState,
   type DataColumn,
 } from "../ui";
 
@@ -247,11 +248,7 @@ export default function Users() {
   };
 
   if (isPending) {
-    return (
-      <div className="admin-loading">
-        <div className="admin-spinner" />
-      </div>
-    );
+    return <LoadingState />;
   }
 
   const columns: DataColumn<User>[] = [