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/Offers.tsx

@@ -34,6 +34,7 @@ import {
   FilterBar,
   Tabs,
   PageHeader,
+  LoadingState,
   type DataColumn,
   type TabDef,
 } from "../ui";
@@ -450,11 +451,7 @@ export default function Offers() {
   };
 
   if (isPending) {
-    return (
-      <div className="admin-loading">
-        <div className="admin-spinner" />
-      </div>
-    );
+    return <LoadingState />;
   }
 
   const total = pagination?.total ?? quotations.length;