refactor(inventory): remove unused fields from InventoryItem and update related DTOs

backend/prisma/migrations/20260418000000_remove_unused_inventory_fields/migration.sql

@@ -0,0 +1,8 @@
+-- Remove unused fields from InventoryItem
+ALTER TABLE `InventoryItem`
+  DROP COLUMN `priority`,
+  DROP COLUMN `shelfNote`,
+  DROP COLUMN `isOnSale`,
+  DROP COLUMN `priceLevel`,
+  DROP COLUMN `proteinType`,
+  DROP COLUMN `isLeftover`;

backend/prisma/schema.prisma

@@ -88,16 +88,10 @@ model InventoryItem {
   brand		 String?
   receiptName    String?
   location       String?
-  priority       Int?
   purchaseDate   DateTime?
   opened         Boolean?
-  shelfNote      String?
   suitableFor    String?
-  isOnSale       Boolean?
-  priceLevel     Int?
-  bestBeforeDate DateTime?	
-  proteinType    String?
-  isLeftover     Boolean?
+  bestBeforeDate DateTime?
   comment        String?
 
   createdAt      DateTime @default(now())