feat(WritePdfBehavior): add WritePdfBehavior to handle PDF writing pipeline

- Implements WritePdfBehavior as an IPipelineBehavior for BurnPdfCommand
- Writes generated PDF to configured export path
- Automatically creates export directory if missing
- Adds logging for export path and file operations

EnvelopeGenerator.Application/DependencyInjection.cs

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

EnvelopeGenerator.Application/Pdf/Behaviors/WritePdfBehavior.cs

@@ -0,0 +1,64 @@
+#if WINDOWS
+using EnvelopeGenerator.Application.Configs;
+using MediatR;
+using Microsoft.Extensions.Logging;
+
+namespace EnvelopeGenerator.Application.Pdf.Behaviors;
+
+/// <summary>
+/// 
+/// </summary>
+public class WritePdfBehavior : IPipelineBehavior<BurnPdfCommand, byte[]>
+{
+    private readonly ISender _sender;
+
+    private readonly ILogger<WritePdfBehavior> _logger;
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="sender"></param>
+    /// <param name="logger"></param>
+    public WritePdfBehavior(ISender sender, ILogger<WritePdfBehavior> logger)
+    {
+        _sender = sender;
+        _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 config = await _sender.ReadDefaultConfigAsync(cancel);
+
+        var exportPath = config.ExportPath ?? throw new InvalidOperationException(nameof(WritePdfBehavior) + " is not possible."
+            + "No export path found in config table.");
+
+        var dirPath = Path.Combine(exportPath, request.Envelope!.Uuid);
+
+        _logger.LogDebug("dirPath is {dirPath}", dirPath);
+
+        if (!Directory.Exists(dirPath))
+        {
+            _logger.LogDebug("Directory not existing. Creating ...");
+            Directory.CreateDirectory(dirPath);
+        }
+
+        var outputFilePath = Path.Combine(dirPath, $"{request.Envelope.Uuid}.pdf");
+
+        _logger.LogDebug("Writing finalized Pdf to disk..");
+        _logger.LogInformation("Output path is {outputFilePath}", outputFilePath);
+
+        await File.WriteAllBytesAsync(outputFilePath, docResult, cancel);
+
+        return docResult;
+    }
+}
+#endif