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.Api/Telegram/TelegramNotifier.cs

@@ -270,7 +270,8 @@ internal sealed class TelegramNotifier(
     public async Task NotifyAdminsPaymentRequestedAsync(
         Guid requestId,
         string userName,
-        PaymentPeriod period,
+        PaymentRequestKind kind,
+        PaymentPeriod? period,
         int amount,
         CancellationToken cancellationToken
     )
@@ -278,8 +279,8 @@ internal sealed class TelegramNotifier(
         if (string.IsNullOrWhiteSpace(options.Value.BotToken))
             return;
 
-        var text =
-            $"💰 <b>{Escape(userName)}</b> заявляет об оплате за {PeriodLabel(period)} — {amount} ₽\nПроверьте поступление и подтвердите.";
+        var reason = kind == PaymentRequestKind.RoleChangeTopUp ? "доплате за смену роли" : $"оплате за {PeriodLabel(period!.Value)}";
+        var text = $"💰 <b>{Escape(userName)}</b> заявляет о {reason} — {amount} ₽\nПроверьте поступление и подтвердите.";
 
         var keyboard = new InlineKeyboardMarkup(
             new[]