feat(Backend): update API gateway and websocket hubs

FinlyticBackend/Hubs/TradeRealtimeHub.cs

@@ -0,0 +1,33 @@
+using System;
+using System.Threading.Tasks;
+using FinlyticCore.Models.Auth;
+using Microsoft.AspNetCore.SignalR;
+using Microsoft.Extensions.Logging;
+
+namespace FinlyticBackend.Hubs;
+
+/// <summary>
+/// Real-time SignalR WebSocket & Server-Sent Events (SSE) Hub streaming live trade proposals & updates to Web and Mobile clients.
+/// </summary>
+public class TradeRealtimeHub : Hub<ITradeClient>
+{
+    private readonly ILogger<TradeRealtimeHub> _logger;
+
+    public TradeRealtimeHub(ILogger<TradeRealtimeHub> logger)
+    {
+        _logger = logger;
+    }
+
+    public override async Task OnConnectedAsync()
+    {
+        _logger.LogInformation("Real-time SignalR Client connected: ConnectionId={ConnectionId}, User={User}",
+            Context.ConnectionId, Context.User?.Identity?.Name ?? "Anonymous");
+        await base.OnConnectedAsync();
+    }
+
+    public override async Task OnDisconnectedAsync(Exception? exception)
+    {
+        _logger.LogInformation("Real-time SignalR Client disconnected: ConnectionId={ConnectionId}", Context.ConnectionId);
+        await base.OnDisconnectedAsync(exception);
+    }
+}