Enhance billing request handling to support immediate config suspension and protection

- Updated the `RejectPaymentRequestCommandHandler` to immediately suspend user configs if a payment request is rejected and no other pending subscription requests exist.
- Introduced `SuspendIfStillUnpaidAsync` method to handle the logic for suspending configs based on the user's billing status.
- Enhanced the `MarkPaymentSentCommandHandler` to protect configs during the payment confirmation process, ensuring users remain active while awaiting admin approval.
- Refactored `BillingConfigResumer` to include methods for protecting and suspending configs, improving the overall billing management flow.
- Updated tests to cover new behaviors and ensure proper functionality in various scenarios related to payment requests and config management.

backend/tests/PnvPanel.Application.Tests/Admin/Billing/ConfirmPaymentRequestCommandHandlerTests.cs

@@ -193,8 +193,9 @@ public class ConfirmPaymentRequestCommandHandlerTests
         Assert.NotNull(expiredConfig.ExpiresAt);
         Assert.NotNull(activeConfig.ExpiresAt);
         Assert.Equal(expiredConfig.ExpiresAt, activeConfig.ExpiresAt);
-        // enable: null — возврат из приостановки теперь идёт через expiresAt (новый newPaidUntil),
-        // а не через переключение enable (см. IXuiPanelGateway.UpdateClientAsync).
+        // enable:true И expiresAt=новый newPaidUntil вместе (см. IXuiPanelGateway.UpdateClientAsync) —
+        // и для ранее Expired конфига (ext-1), и для уже Active (ext-2): пользователь мог доплатить
+        // заранее, панель должна узнать новый срок сразу, а не только когда конфиг реально просрочится.
         await _gateway
             .Received(1)
             .UpdateClientAsync(
@@ -203,10 +204,22 @@ public class ConfirmPaymentRequestCommandHandlerTests
                 "ext-1",
                 VpnProtocol.Vless,
                 Arg.Any<string>(),
-                null,
+                true,
                 Arg.Is<DateTimeOffset?>(d => d == expiredConfig.ExpiresAt),
                 Arg.Any<CancellationToken>()
             );
+        await _gateway
+            .Received(1)
+            .UpdateClientAsync(
+                Arg.Any<Node>(),
+                inbound.RemoteInboundId,
+                "ext-2",
+                VpnProtocol.Vless,
+                Arg.Any<string>(),
+                true,
+                Arg.Is<DateTimeOffset?>(d => d == activeConfig.ExpiresAt),
+                Arg.Any<CancellationToken>()
+            );
     }
 
     [Fact]