Refactor payment request handling to support role change top-ups

- Updated the `PaymentRequest` model to include a new `Kind` property, distinguishing between `Subscription` and `RoleChangeTopUp` requests.
- Modified the `TelegramNotifier` to accommodate the new request type, ensuring accurate notifications for role change top-ups.
- Enhanced the `ConfirmPaymentRequestCommandHandler` to handle role change top-ups without extending the billing period, reflecting the new payment logic.
- Updated various application components and tests to support the new payment request structure and ensure proper functionality.
- Revised API documentation to clarify the behavior of role change top-ups and their impact on billing.

backend/src/PnvPanel.Application/Common/Interfaces/ITelegramNotifier.cs

@@ -54,11 +54,13 @@ public interface ITelegramNotifier
     );
 
     /// <summary>Пользователь нажал «Я оплатил» — инлайн-кнопки «Подтвердить/Отклонить», решается
-    /// полностью в Telegram (аналогично заявке на роль).</summary>
+    /// полностью в Telegram (аналогично заявке на роль). Period задан только для Kind.Subscription —
+    /// для Kind.RoleChangeTopUp он null (доплата не привязана к тарифному периоду).</summary>
     Task NotifyAdminsPaymentRequestedAsync(
         Guid requestId,
         string userName,
-        PaymentPeriod period,
+        PaymentRequestKind kind,
+        PaymentPeriod? period,
         int amount,
         CancellationToken cancellationToken
     );