Added scalar api reference

Successful local run

LiteCharmsMessaging/Program.cs

@@ -1,11 +1,13 @@
 using Microsoft.AspNetCore.Mvc;
 using MimeKit;
+using Scalar.AspNetCore;
 using SmtpClient = MailKit.Net.Smtp.SmtpClient;
 
 var builder = WebApplication.CreateBuilder(args);
 
 var allowedOrigins = builder.Configuration.GetSection("CorsSettings:AllowedOrigins").Get<string[]>() ?? Array.Empty<string>();
 
+builder.Services.AddOpenApi();
 builder.Services.AddCors(options =>
 {
     options.AddPolicy("AllowStrictOrigins", policy =>
@@ -34,7 +36,7 @@ app.MapPost("/api/send-email", async ([FromBody] EmailRequest request, IConfigur
 
         message.From.Add(MailboxAddress.Parse(fromAddress!));
         message.To.Add(MailboxAddress.Parse(toAddress!));
-        message.Subject = "New message from LiteCharms";
+        message.Subject = string.IsNullOrWhiteSpace(request.Subject) ? "New message from LiteCharms" : request.Subject;
 
         var bodyBuilder = new BodyBuilder { HtmlBody = request.HtmlBody };
         message.Body = bodyBuilder.ToMessageBody();
@@ -60,4 +62,7 @@ app.MapPost("/api/send-email", async ([FromBody] EmailRequest request, IConfigur
     }
 });
 
+app.MapOpenApi();
+app.MapScalarApiReference();
+
 app.Run();