Add Telegram bot integration and enhance user management features

- Introduced Telegram.Bot package for bot functionality.
- Updated user management to include Telegram linking and blocking features.
- Enhanced activation request handling with notifications via Telegram.
- Added new database entities for Telegram link tokens and login requests.
- Implemented traffic synchronization for client stats in the XuiPanelGateway.
- Updated application structure to support new test projects and improved dependency injection for Telegram services.

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

@@ -0,0 +1,15 @@
+namespace PnvPanel.Application.Common.Interfaces;
+
+/// <summary>
+/// Проактивные DM-уведомления через бота. Реализация — в Api (нужен ITelegramBotClient,
+/// который там же и регистрируется), аналогично IRealtimeNotifier/PanelHub. Если BotToken не
+/// задан — реализация тихо не отправляет ничего (бот работает без Telegram).
+/// </summary>
+public interface ITelegramNotifier
+{
+    Task NotifyAdminsActivationRequestedAsync(
+        Guid requestId, string userName, string? comment, CancellationToken cancellationToken);
+
+    /// <summary>Личное сообщение пользователю, если у него привязан Telegram (иначе no-op).</summary>
+    Task NotifyUserAsync(Guid userId, string message, CancellationToken cancellationToken);
+}