Add news feature with CRUD operations and real-time notifications

- Implemented news management functionality, allowing admins to create, read, update, and delete news posts.
- Introduced a new SignalR event for broadcasting news updates to all connected clients.
- Updated API documentation to include new endpoints for news management.
- Enhanced frontend with a dedicated news page and admin interface for managing news posts.
- Added necessary localization for news-related terms in both Russian and English.

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

@@ -5,6 +5,7 @@ using PnvPanel.Domain.Apps;
 using PnvPanel.Domain.Audit;
 using PnvPanel.Domain.Configs;
 using PnvPanel.Domain.Inbounds;
+using PnvPanel.Domain.News;
 using PnvPanel.Domain.Nodes;
 using PnvPanel.Domain.Telegram;
 
@@ -30,6 +31,8 @@ public interface IAppDbContext
 
     DbSet<ClientApp> ClientApps { get; }
 
+    DbSet<NewsPost> NewsPosts { get; }
+
     /// <summary>Нужен для advisory-lock при проверке квоты конфигов (см. CreateVpnConfigCommandHandler).</summary>
     DatabaseFacade Database { get; }