Add notification for ticket reopening to Telegram admins

- Implemented NotifyAdminsTicketReopenedAsync method in TelegramNotifier to notify admins when a ticket is reopened, including a link to the ticket on the public site.
- Updated ITelegramNotifier interface to include the new notification method.
- Modified ReopenTicketCommandHandler to invoke the new notification method after a ticket is reopened.
- Enhanced unit tests for ReopenTicketCommandHandler to verify the notification functionality.

backend/src/PnvPanel.Application/Support/Reopen/ReopenTicketCommandHandler.cs

@@ -7,7 +7,7 @@ using PnvPanel.Domain.Support;
 
 namespace PnvPanel.Application.Support.Reopen;
 
-public sealed class ReopenTicketCommandHandler(IAppDbContext dbContext, ICurrentUser currentUser)
+public sealed class ReopenTicketCommandHandler(IAppDbContext dbContext, ITelegramNotifier telegramNotifier, ICurrentUser currentUser)
     : ICommandHandler<ReopenTicketCommand, Result>
 {
     public async Task<Result> Handle(ReopenTicketCommand command, CancellationToken cancellationToken)
@@ -24,6 +24,10 @@ public sealed class ReopenTicketCommandHandler(IAppDbContext dbContext, ICurrent
             return Result.Failure(SupportErrors.NotResolved);
 
         ticket.Reopen();
+
+        var userName = currentUser.UserName ?? userId.ToString();
+        await telegramNotifier.NotifyAdminsTicketReopenedAsync(ticket.Id, userName, ticket.Type, cancellationToken);
+
         return Result.Success();
     }
 }