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.Api/Identity/ApplicationDbContext.cs

@@ -0,0 +1,8 @@
+using Microsoft.AspNetCore.Identity.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore;
+
+namespace Shogi.Api.Identity;
+
+public class ApplicationDbContext(DbContextOptions<ApplicationDbContext> options) : IdentityDbContext<ShogiUser>(options)
+{
+}