feat(SendEmailBehavior): add SendEmailBehavior for sending final emails after PDF burn

- Implements IPipelineBehavior<BurnPdfCommand, byte[]> to send emails to creator and receivers.
- Logs debug information when sending emails and warnings if email sending is skipped.
- Uses Envelope's FinalEmailType to determine whether to send emails.

EnvelopeGenerator.Application/DependencyInjection.cs

@@ -91,6 +91,7 @@ public static class DependencyInjection
             cfg.AddBehavior<CreateHistoryBehavior>();
             cfg.AddBehavior<SavePdfBehavior>();
 #if WINDOWS
+            cfg.AddBehavior<SendEmailBehavior>();
             cfg.AddBehavior<WritePdfBehavior>();
             cfg.AddBehavior<PdfMergeBehavior>();
             cfg.AddBehavior<AddReportBehavior>();

EnvelopeGenerator.Application/Pdf/Behaviors/SendEmailBehavior.cs

@@ -0,0 +1,61 @@
+using EnvelopeGenerator.Domain.Constants;
+using MediatR;
+using Microsoft.Extensions.Logging;
+
+namespace EnvelopeGenerator.Application.Pdf.Behaviors;
+
+/// <summary>
+/// 
+/// </summary>
+public class SendEmailBehavior : IPipelineBehavior<BurnPdfCommand, byte[]>
+{
+    private readonly ILogger<SendEmailBehavior> _logger;
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="logger"></param>
+    public SendEmailBehavior(ILogger<SendEmailBehavior> logger)
+    {
+        _logger = logger;
+    }
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="request"></param>
+    /// <param name="next"></param>
+    /// <param name="cancel"></param>
+    /// <returns></returns>
+    public async Task<byte[]> Handle(BurnPdfCommand request, RequestHandlerDelegate<byte[]> next, CancellationToken cancel)
+    {
+        var docResult = await next(cancel);
+
+        var mailToCreator = request.Envelope!.FinalEmailToCreator;
+        var mailToReceivers = request.Envelope.FinalEmailToReceivers;
+
+        if (mailToCreator is not null && mailToCreator != (int)FinalEmailType.No)
+        {
+            _logger.LogDebug("Sending email to creator ...");
+            SendFinalEmailToCreator(request.Envelope); // , pAttachment
+        }
+        else
+        {
+            _logger.LogWarning("No SendFinalEmailToCreator - mailToCreator [{mailToCreator}] <> [{FinalEmailType.No}] ", 
+                mailToCreator, FinalEmailType.No);
+        }
+
+        if (mailToReceivers != (int)FinalEmailType.No)
+        {
+            _logger.LogDebug("Sending emails to receivers...");
+            SendFinalEmailToReceivers(request.Envelope); // , pAttachment
+        }
+        else
+        {
+            _logger.LogWarning("No SendFinalEmailToReceivers - mailToReceivers [{mailToReceivers}] <> [{FinalEmailType.No}] ", 
+                mailToReceivers, FinalEmailType.No);
+        }
+
+        return docResult;
+    }
+}