fix(documents): include custom-field selection in offer/issued-order unsaved-changes guard

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/admin/pages/IssuedOrderDetail.tsx

@@ -260,7 +260,7 @@ export default function IssuedOrderDetail() {
   const canExport = hasPermission("orders.view");
 
   const { isDirty, markClean } = useUnsavedChangesGuard(
-    { form, items, sections },
+    { form, items, sections, selectedCustomFields },
     !isEdit || dataReady,
   );
 

src/admin/pages/OfferDetail.tsx

@@ -275,7 +275,7 @@ export default function OfferDetail() {
   const canDelete = isEdit && !orderInfo && !isInvalidated && !isLockedByOther;
 
   const { markClean } = useUnsavedChangesGuard(
-    { form, items, sections },
+    { form, items, sections, selectedCustomFields },
     !loading,
   );