Update dlibPath to use dynamic base directory path

Previously, the `dlibPath` variable was hardcoded as a relative
path. This commit updates it to dynamically construct the path
using `AppDomain.CurrentDomain.BaseDirectory` and appending the
relative path. This change improves robustness and ensures the
path resolves correctly in different execution environments.

Author: michaelmsonne

src/SignToolGUI/Forms/MainForm.cs

@@ -1364,7 +1364,7 @@ private async Task SignWithTrustedSigningAsync()
                 }
             }
 
-            var dlibPath = @".\Tools\Azure.CodeSigning.Dlib.dll";
+            var dlibPath = AppDomain.CurrentDomain.BaseDirectory + "Tools\\Azure.CodeSigning.Dlib.dll";
             var codeSigningAccountName = textBoxCodeSigningAccountName.Text;
             var certificateProfileName = textBoxCertificateProfileName.Text;
             var correlationIdData = textBoxCorrelationId.Text;