Replace custom socket implementation with SignalR.

Replace MSAL and custom cookie auth with Microsoft.Identity.EntityFramework
Also some UI redesign to accommodate different login experience.

Shogi.Contracts/Types/Session.cs

@@ -1,9 +1,20 @@
-namespace Shogi.Contracts.Types;
+using System;
+
+namespace Shogi.Contracts.Types;
 
 public class Session
 {
-	public User Player1 { get; set; }
-	public User? Player2 { get; set; }
-	public string SessionName { get; set; }
+	/// <summary>
+	/// Email
+	/// </summary>
+	public string Player1 { get; set; }
+
+	/// <summary>
+	/// Email. Null if no second player exists.
+	/// </summary>
+	public string? Player2 { get; set; }
+
+	public Guid SessionId { get; set; }
+
 	public BoardState BoardState { get; set; }
 }