Introduced FlatPaymentController under Distribution.Features.Payment, providing GET and POST endpoints at /api/payments. Supports listing, retrieving, and creating payments with filtering and error handling. Business logic is delegated to PaymentService.
Implemented DeliveryTask, Payment, and Sale entities with full CRUD, business logic, and API endpoints. Updated Order/OrderItem for sale linkage and fulfillment tracking. Registered new DbSets and DI services. Revised documentation for delivery, sale, and payment workflows.