fix(tests): skip cut-time PDF test when pdftotext is missing

The GitHub Linux runner has no poppler-utils, so ReportPdf throws
SkipException; as a plain [Fact] the test failed instead of skipping.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

OpenNest.Tests/Reporting/NestPdfWriterTests.cs

@@ -207,7 +207,7 @@ public sealed class NestPdfWriterTests : IDisposable
 
     public void Dispose() => Directory.Delete(directory, true);
 
-    [Fact]
+    [SkippableFact]
     public void Write_CutTimeEstimateAppearsOnSummaryAndPlatePages()
     {
         var path = Path.Combine(directory, "timed.report.pdf");