Implement billing functionality and enhance role management

- Introduced billing capabilities, allowing users to request payments for subscription periods (3/6/12 months) with admin approval via Telegram.
- Updated role management to include a `BillingEnabled` property, preventing billing for admin roles.
- Enhanced the `CreateRoleCommand` and `UpdateRoleCommand` to accept billing parameters, ensuring proper handling during role creation and updates.
- Added new endpoints for billing management and integrated billing checks into VPN config creation to enforce payment requirements.
- Updated related services, models, and tests to support the new billing features, ensuring comprehensive coverage and functionality.
- Enhanced documentation to reflect the new billing processes and role management changes.

backend/src/PnvPanel.Application/Billing/MarkPaymentSent/MarkPaymentSentCommandHandler.cs

@@ -0,0 +1,45 @@
+using Microsoft.EntityFrameworkCore;
+using PnvPanel.Application.Auth;
+using PnvPanel.Application.Common.Interfaces;
+using PnvPanel.Application.Common.Messaging;
+using PnvPanel.Application.Common.Models;
+using PnvPanel.Domain.Billing;
+
+namespace PnvPanel.Application.Billing.MarkPaymentSent;
+
+public sealed class MarkPaymentSentCommandHandler(
+    IAppDbContext dbContext,
+    IIdentityService identityService,
+    ITelegramNotifier telegramNotifier,
+    ICurrentUser currentUser
+) : ICommandHandler<MarkPaymentSentCommand, Result>
+{
+    public async Task<Result> Handle(MarkPaymentSentCommand command, CancellationToken cancellationToken)
+    {
+        if (currentUser.UserId is not { } userId)
+            return Result.Failure(AuthErrors.Unauthorized);
+
+        var request = await dbContext.PaymentRequests.FirstOrDefaultAsync(
+            r => r.Id == command.RequestId && r.UserId == userId,
+            cancellationToken
+        );
+        if (request is null)
+            return Result.Failure(BillingErrors.RequestNotFound);
+
+        if (request.Status != PaymentRequestStatus.AwaitingPayment)
+            return Result.Failure(BillingErrors.RequestNotAwaitingPayment);
+
+        request.MarkPaymentSent();
+
+        var profile = await identityService.GetProfileAsync(userId, cancellationToken);
+        await telegramNotifier.NotifyAdminsPaymentRequestedAsync(
+            request.Id,
+            profile?.UserName ?? userId.ToString(),
+            request.Period,
+            request.AmountSnapshot,
+            cancellationToken
+        );
+
+        return Result.Success();
+    }
+}