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.Infrastructure/Persistence/AppDbContext.cs

@@ -6,6 +6,7 @@ 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;
 using PnvPanel.Infrastructure.Identity;
@@ -39,6 +40,8 @@ public class AppDbContext(DbContextOptions<AppDbContext> options)
 
     public DbSet<ClientApp> ClientApps => Set<ClientApp>();
 
+    public DbSet<NewsPost> NewsPosts => Set<NewsPost>();
+
     protected override void OnModelCreating(ModelBuilder modelBuilder)
     {
         base.OnModelCreating(modelBuilder);