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/Admin/News/CreatePostCommandHandler.cs

@@ -0,0 +1,21 @@
+using PnvPanel.Application.Common.Interfaces;
+using PnvPanel.Application.Common.Messaging;
+using PnvPanel.Application.Common.Models;
+using PnvPanel.Application.News;
+using PnvPanel.Domain.News;
+
+namespace PnvPanel.Application.Admin.News;
+
+public sealed class CreatePostCommandHandler(IAppDbContext dbContext, IRealtimeNotifier notifier)
+    : ICommandHandler<CreatePostCommand, Result<NewsPostDto>>
+{
+    public async Task<Result<NewsPostDto>> Handle(CreatePostCommand command, CancellationToken cancellationToken)
+    {
+        var post = NewsPost.Create(command.Title, command.Body);
+        dbContext.NewsPosts.Add(post);
+
+        await notifier.NotifyNewsPublishedAsync(post.Id, post.Title, post.CreatedAt, cancellationToken);
+
+        return Result.Success(NewsPostDto.FromDomain(post));
+    }
+}