feat: complete SaaS commercial delivery workflows

Tiku.Infrastructure/Commerce/ManualPaymentProvider.cs

@@ -38,4 +38,24 @@ internal sealed class ManualPaymentProvider : IPaymentProvider
             "Manual payment does not accept provider notifications.",
             "manual_payment_notification_not_supported");
     }
+
+    public Task<CreateRefundProviderResult> CreateRefundAsync(
+        PaymentProviderAccount account,
+        CreateRefundProviderRequest request,
+        CancellationToken cancellationToken = default)
+    {
+        cancellationToken.ThrowIfCancellationRequested();
+        var payload = JsonSerializer.SerializeToElement(new
+        {
+            request.OrderNo,
+            request.RefundNo,
+            request.AmountCents,
+            request.Reason
+        });
+        return Task.FromResult(new CreateRefundProviderResult(
+            Provider,
+            true,
+            $"manual-{request.RefundNo}",
+            payload));
+    }
 }