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.Domain/News/NewsPost.cs

@@ -0,0 +1,34 @@
+using PnvPanel.Domain.Common;
+
+namespace PnvPanel.Domain.News;
+
+/// <summary>Новость, которую публикует админ. Публикация мгновенная — нет статуса черновик/опубликовано.</summary>
+public sealed class NewsPost : Entity
+{
+    public string Title { get; private set; } = string.Empty;
+    public string Body { get; private set; } = string.Empty;
+    public DateTimeOffset CreatedAt { get; private set; }
+    public DateTimeOffset? UpdatedAt { get; private set; }
+
+    private NewsPost()
+    {
+    }
+
+    public static NewsPost Create(string title, string body)
+    {
+        return new NewsPost
+        {
+            Id = Guid.NewGuid(),
+            Title = title,
+            Body = body,
+            CreatedAt = DateTimeOffset.UtcNow,
+        };
+    }
+
+    public void Update(string title, string body)
+    {
+        Title = title;
+        Body = body;
+        UpdatedAt = DateTimeOffset.UtcNow;
+    }
+}