feat: add salePrice field to Product model and update related files

- Added salePrice field to Product model in Prisma schema and generated files.
- Updated Product scalar field enums in both TypeScript files.
- Modified aggregate output types to include salePrice.
- Enhanced input types for creating and updating products to support salePrice.
- Updated migration file to add salePrice column to Products table.
- Created DTOs for inventory management in POS module.
- Implemented POS controller and service with methods for stock and product categories.

prisma/schema.prisma

@@ -70,6 +70,7 @@ model Product {
   createdAt              DateTime                @default(now()) @db.Timestamp(0)
   updatedAt              DateTime                @updatedAt @db.Timestamp(0)
   deletedAt              DateTime?               @db.Timestamp(0)
+  salePrice              Decimal                 @default(0.00) @db.Decimal(10, 2)
   brandId                Int?
   categoryId             Int?
   inventoryTransferItems InventoryTransferItem[] @relation("InventoryTransferItem_Product")