feat(Backend): update API gateway and websocket hubs

FinlyticBackend/Hubs/NewsHub.cs

@@ -0,0 +1,22 @@
+using Microsoft.AspNetCore.SignalR;
+using System.Threading.Tasks;
+using FinlyticCore.Dtos.News;
+
+namespace FinlyticBackend.Hubs;
+
+/// <summary>
+/// SignalR Hub for real-time news delivery to connected clients.
+/// </summary>
+public class NewsHub : Hub
+{
+    // Clients can call this to join specific symbol groups if needed later
+    public async Task SubscribeToSymbol(string symbol)
+    {
+        await Groups.AddToGroupAsync(Context.ConnectionId, symbol.ToUpperInvariant());
+    }
+
+    public async Task UnsubscribeFromSymbol(string symbol)
+    {
+        await Groups.RemoveFromGroupAsync(Context.ConnectionId, symbol.ToUpperInvariant());
+    }
+}