shared catalog in Bestellungen, catalog picker in line items, Ersatzbeschaffung flag, vendor detail flash fix

frontend/src/pages/LieferantDetail.tsx

@@ -48,7 +48,7 @@ export default function LieferantDetail() {
   const [deleteDialogOpen, setDeleteDialogOpen] = useState(false);
 
   // ── Query ──
-  const { data: vendor, isLoading, isError } = useQuery({
+  const { data: vendor, isPending, isLoading, isError } = useQuery({
     queryKey: ['lieferant', vendorId],
     queryFn: () => bestellungApi.getVendor(vendorId),
     enabled: !isNew && !!vendorId,
@@ -128,7 +128,7 @@ export default function LieferantDetail() {
   }
 
   // ── Loading / Error ──
-  if (!isNew && isLoading) {
+  if (!isNew && isPending) {
     return (
       <DashboardLayout>
         <Box sx={{ display: 'flex', alignItems: 'center', gap: 2, mb: 3 }}>
@@ -144,7 +144,7 @@ export default function LieferantDetail() {
     );
   }
 
-  if (!isNew && (isError || !vendor)) {
+  if (!isNew && !isPending && (isError || !vendor)) {
     return (
       <DashboardLayout>
         <Box sx={{ p: 4, textAlign: 'center' }}>