feat: implement cross-device reading progress synchronization using SignalR and remove legacy quiz generation services.

src/NexusReader.Infrastructure/RealTime/SyncHub.cs

@@ -0,0 +1,46 @@
+using MediatR;
+using Microsoft.AspNetCore.SignalR;
+using Microsoft.AspNetCore.Authorization;
+using NexusReader.Application.Commands.Sync;
+
+namespace NexusReader.Infrastructure.RealTime;
+
+[Authorize]
+public class SyncHub : Hub
+{
+    private readonly IMediator _mediator;
+
+    public SyncHub(IMediator mediator)
+    {
+        _mediator = mediator;
+    }
+
+    public async Task UpdateProgress(string pageId)
+    {
+        var userId = Context.UserIdentifier;
+        if (!string.IsNullOrEmpty(userId))
+        {
+            await _mediator.Send(new UpdateReadingProgressCommand(pageId, userId));
+        }
+    }
+
+    public override async Task OnConnectedAsync()
+    {
+        var userId = Context.UserIdentifier;
+        if (!string.IsNullOrEmpty(userId))
+        {
+            await Groups.AddToGroupAsync(Context.ConnectionId, $"User_{userId}");
+        }
+        await base.OnConnectedAsync();
+    }
+
+    public override async Task OnDisconnectedAsync(Exception? exception)
+    {
+        var userId = Context.UserIdentifier;
+        if (!string.IsNullOrEmpty(userId))
+        {
+            await Groups.RemoveFromGroupAsync(Context.ConnectionId, $"User_{userId}");
+        }
+        await base.OnDisconnectedAsync(exception);
+    }
+}