Allow null price and unlimited stock on store item create/sync.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/store/store-items.service.ts

@@ -916,11 +916,11 @@ export class StoreItemsService {
     existingKeys.add(key);
     batchKeys.add(key);
 
-    if (item.price !== undefined && item.price < 0) {
+    if (item.price != null && item.price < 0) {
       throw new BadRequestException('Price cannot be negative');
     }
 
-    if (item.stockQuantity !== undefined && item.stockQuantity < 0) {
+    if (item.stockQuantity != null && item.stockQuantity < 0) {
       throw new BadRequestException('Stock cannot be negative');
     }
   }