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/migrations/20251214090742_init/migration.sql

@@ -0,0 +1,2 @@
+-- AlterTable
+ALTER TABLE `Products` ADD COLUMN `salePrice` DECIMAL(10, 2) NOT NULL DEFAULT 0.00;