Add conditional Windows Service & Kestrel config support

The app now checks configuration values to optionally run as a Windows Service ("UseWindowsService") and/or apply custom Kestrel server settings from the "Kestrel" config section ("UseKestrelConfig"). These changes improve deployment flexibility.

EnvelopeGenerator.ServiceHost/Program.cs

@@ -9,7 +9,21 @@ using System.Globalization;
 
 var builder = WebApplication.CreateBuilder(args);
 
-// Add services to the container.
+#region Kestrel & Windows Service Configuration
+if (builder.Configuration.GetValue<bool>("UseWindowsService"))
+{
+    builder.Host.UseWindowsService();
+}
+
+if (builder.Configuration.GetValue<bool>("UseKestrelConfig"))
+{
+    builder.WebHost.ConfigureKestrel((context, serverOptions) =>
+    {
+        var kestrelSection = context.Configuration.GetSection("Kestrel");
+        serverOptions.Configure(kestrelSection);
+    });
+}
+#endregion
 
 var config = builder.Configuration;
 var connStr = config.GetConnectionString("Default") ??
@@ -76,4 +90,4 @@ app.UseAuthorization();
 
 app.MapControllers();
 
-app.Run();
+app.Run();