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/Repositories/EmailSender.cs

@@ -0,0 +1,54 @@
+using Microsoft.AspNetCore.Identity.UI.Services;
+using Microsoft.Extensions.Options;
+using System.Net.Http.Headers;
+using System.Text.Json;
+
+namespace Shogi.Api.Repositories;
+
+// https://app-smtp.brevo.com/real-time
+
+public class EmailSender : IEmailSender
+{
+	private static readonly JsonSerializerOptions Options = new(JsonSerializerDefaults.Web);
+	private readonly HttpClient client;
+	private string apiKey;
+
+
+	public EmailSender(HttpClient client, IOptionsMonitor<ApiKeys> apiKeys)
+	{
+		this.apiKey = apiKeys.CurrentValue.BrevoEmailService;
+		apiKeys.OnChange(keys => this.apiKey = keys.BrevoEmailService);
+		this.client = client;
+	}
+
+
+	public async Task SendEmailAsync(string email, string subject, string htmlMessage)
+	{
+		var body = new
+		{
+			Sender = new
+			{
+				Name = "Shogi Account Support",
+				Email = "shogi@lucaserver.space",
+			},
+			To = new[]
+			{
+				new
+				{
+					Name = email,
+					Email = email,
+				}
+			},
+			Subject = subject,
+			HtmlContent = htmlMessage,
+		};
+
+		var request = new HttpRequestMessage(HttpMethod.Post, new Uri("https://api.brevo.com/v3/smtp/email", UriKind.Absolute));
+		request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
+		request.Headers.Add("api-key", apiKey);
+		request.Content = JsonContent.Create(body, options: Options);
+
+		var response = await this.client.SendAsync(request);
+		response.EnsureSuccessStatusCode();
+	}
+}