refactor(flyer-import): improve displayNameDetailed handling

- Simplified conditional logic for displayNameDetailed assignment
- Added fallback to preserve existing value when displayNameDetailed is falsy
- Reformatted multi-line object initialization for better readability

backend/src/flyer-import/flyer-import.service.ts

@@ -889,13 +889,14 @@ export class FlyerImportService {
       bundleWeight: item.bundleWeight,
       isBundle: item.isBundle,
       bundleItems: this.sanitizeBundleItems(toStringArray(item.bundleItems)),
-      displayNameDetailed:
-        item.displayNameDetailed ?
-        buildDisplayNameDetailed({
-          rawName: item.rawName,
-          isBundle: item.isBundle,
-          bundleItems: this.sanitizeBundleItems(toStringArray(item.bundleItems)),
-        }),
+       displayNameDetailed:
+         item.displayNameDetailed
+           ? buildDisplayNameDetailed({
+               rawName: item.rawName,
+               isBundle: item.isBundle,
+               bundleItems: this.sanitizeBundleItems(toStringArray(item.bundleItems)),
+             })
+           : item.displayNameDetailed,
       signals: toSignals(item.signals),
       offerText: item.offerText,
       isOffer: