feat: implement save receipt functionality with transaction handling and DTOs

backend/prisma/migrations/20260509000000_remove_product_category_and_add_indexes/migration.sql

@@ -0,0 +1,5 @@
+-- AlterTable: Remove Product.category field (redundant with categoryId)
+ALTER TABLE `Product` DROP COLUMN `category`;
+
+-- AlterTable: Add index on ReceiptAlias.receiptName for faster lookups
+CREATE INDEX `ReceiptAlias_receiptName_idx` ON `ReceiptAlias`(`receiptName`);

backend/prisma/schema.prisma

@@ -36,7 +36,6 @@ model Product {
   id             Int             @id @default(autoincrement())
   name           String
   normalizedName String          @unique
-  category       String?
   canonicalName  String?
   isActive       Boolean         @default(true)
   status         String           @default("active")
@@ -201,6 +200,7 @@ model ReceiptAlias {
   @@unique([receiptName, ownerId, isGlobal])
   @@index([ownerId])
   @@index([isGlobal])
+  @@index([receiptName])
 }
 
 model MealPlanEntry {