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/Telegram/TelegramErrors.cs

@@ -0,0 +1,15 @@
+using PnvPanel.Application.Common.Models;
+
+namespace PnvPanel.Application.Telegram;
+
+public static class TelegramErrors
+{
+    public static readonly Error LinkTokenNotFound =
+        Error.NotFound("Telegram.LinkTokenNotFound", "Токен привязки не найден или истёк.");
+
+    public static readonly Error LoginRequestNotFound =
+        Error.NotFound("Telegram.LoginRequestNotFound", "Запрос на вход не найден.");
+
+    public static readonly Error NotLinked =
+        Error.Conflict("Telegram.NotLinked", "Telegram не привязан ни к одному аккаунту.");
+}