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.Infrastructure/Persistence/Configurations/AppUserConfiguration.cs

@@ -0,0 +1,15 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+using PnvPanel.Infrastructure.Identity;
+
+namespace PnvPanel.Infrastructure.Persistence.Configurations;
+
+public class AppUserConfiguration : IEntityTypeConfiguration<AppUser>
+{
+    public void Configure(EntityTypeBuilder<AppUser> builder)
+    {
+        // Уникален среди привязанных (Postgres не считает NULL равным NULL — обычный unique подходит).
+        builder.HasIndex(x => x.TelegramUserId).IsUnique();
+        builder.HasIndex(x => x.SubscriptionToken).IsUnique();
+    }
+}