feat(customers): add DTOs for individual and legal customer creation

- Created CreateCustomerIndividualDto for individual customer data with fields: first_name, last_name, national_code, postal_code, is_favorite, and economic_code.
- Created CreateCustomerLegalDto for legal customer data with fields: company_name, economic_code, registration_number, and postal_code.

prisma/migrations/20260221124338_init/migration.sql

@@ -0,0 +1,3 @@
+-- AlterTable
+ALTER TABLE `sales_invoice_items` ADD COLUMN `discount` DECIMAL(15, 2) NOT NULL DEFAULT 0.00,
+    ADD COLUMN `pricingModel` ENUM('STANDARD', 'GOLD') NOT NULL DEFAULT 'STANDARD';