Add DeliveryTask, Payment, and Sale features

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.

Distribution/Features/Payment/PaymentController.cs

@@ -0,0 +1,28 @@
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+
+namespace Distribution.Features.Payment;
+
+[ApiController]
+[Authorize]
+[Route("api/sales/{saleId:guid}/payments")]
+public class PaymentController(PaymentService service) : ControllerBase
+{
+    [HttpGet]
+    public async Task<IActionResult> GetBySale(Guid saleId)
+    {
+        var result = await service.GetBySaleIdAsync(saleId);
+        return result is null ? NotFound() : Ok(result);
+    }
+
+    [HttpPost]
+    public async Task<IActionResult> Create(Guid saleId, CreatePaymentRequest request, CancellationToken ct)
+    {
+        try
+        {
+            var result = await service.CreateAsync(saleId, request, ct);
+            return result is null ? NotFound() : Ok(result);
+        }
+        catch (InvalidOperationException ex) { return BadRequest(new { error = ex.Message }); }
+    }
+}