feat(Backend): update API gateway and websocket hubs

FinlyticBackend/Hubs/TradeHub.cs

@@ -0,0 +1,14 @@
+using Microsoft.AspNetCore.SignalR;
+
+namespace FinlyticBackend.Hubs;
+
+/// <summary>
+/// SignalR Hub broadcasting real-time trade signals, position updates, and closed trade events.
+/// </summary>
+public class TradeHub : Hub
+{
+    public override async Task OnConnectedAsync()
+    {
+        await base.OnConnectedAsync();
+    }
+}