feat: add Scalar API reference UI

- Scalar.AspNetCore 2.14.9
- Available in Development at /scalar/v1
- Theme: DeepSpace

Ref: IT-628

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

HrynCo.NotificationService.Api/Program.cs

@@ -1,6 +1,7 @@
 using HrynCo.NotificationService.Api;
 using HrynCo.NotificationService.DAL.EF;
 using HrynCo.NotificationService.Services;
+using Scalar.AspNetCore;
 
 var builder = WebApplication.CreateBuilder(args);
 
@@ -19,7 +20,14 @@ builder.Services.AddNotificationServices();
 var app = builder.Build();
 
 if (app.Environment.IsDevelopment())
+{
     app.MapOpenApi();
+    app.MapScalarApiReference(options =>
+    {
+        options.Title = "HrynCo Notification Service";
+        options.Theme = ScalarTheme.DeepSpace;
+    });
+}
 
 app.UseHttpsRedirection();
 app.MapControllers();