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/PlanWork.tsx

@@ -15,7 +15,7 @@ import PlanGrid from "../components/PlanGrid";
 import PlanCellModal from "../components/PlanCellModal";
 import PlanCategoriesModal from "../components/PlanCategoriesModal";
 import Forbidden from "../components/Forbidden";
-import { Button, Alert } from "../ui";
+import { Button, Alert, LoadingState } from "../ui";
 import { projectListOptions, type Project } from "../lib/queries/projects";
 import { planCategoriesOptions, type PlanCategory } from "../lib/queries/plan";
 // plan.css is imported once globally in AdminApp.tsx — no per-page re-import.
@@ -670,11 +670,7 @@ export default function PlanWork() {
         </Box>
       </motion.div>
 
-      {gridLoading && (
-        <div className="admin-loading">
-          <div className="admin-spinner" />
-        </div>
-      )}
+      {gridLoading && <LoadingState />}
 
       {/*
         Grid entrance: same pattern as the h1 / banner / toolbar above