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/Vehicles.tsx

@@ -20,6 +20,7 @@ import {
   Field,
   TextField,
   SwitchField,
+  LoadingState,
   type DataColumn,
 } from "../ui";
 
@@ -222,11 +223,7 @@ export default function Vehicles() {
   };
 
   if (isPending) {
-    return (
-      <div className="admin-loading">
-        <div className="admin-spinner" />
-      </div>
-    );
+    return <LoadingState />;
   }
 
   const columns: DataColumn<Vehicle>[] = [