[UI] Fix "assign to customer" (#11151)

- Hide if base part is not salable
- Closes https://github.com/inventree/InvenTree/issues/11134

src/frontend/src/pages/stock/StockDetail.tsx

@@ -753,7 +753,7 @@ export default function StockDetail() {
   const stockAdjustActions = useStockAdjustActions({
     formProps: stockOperationProps,
     delete: false,
-    assign: !!stockitem.in_stock,
+    assign: !!stockitem.in_stock && stockitem.part_detail?.salable,
     return: !!stockitem.consumed_by || !!stockitem.customer,
     merge: false
   });