feat: improve DXF export and cross-platform file handling

- PepSettings: add DrawingsDirectory property for DXF endpoint config
- DrawingDxfExporter: support subprogram calls, skip non-cut linear moves,
  remove spurious radians-to-degrees conversion on arc angles, set AC1018 DXF version
- DrawingReader: handle .loop-info/.cadsnapshot entries gracefully, derive
  DrawingInfo from loop names when .info entry is absent, use FileShare.Read
- DrawingInfoReader: use TryParse instead of Parse for material number
- Drawing: make GetLoopName public (used by DrawingDxfExporter)
- ZipHelper: use FileShare.Read to allow concurrent readers on Windows/Linux
- NestFilterData: skip status filter when value is "All"

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

PepLib.Core/IO/DrawingInfoReader.cs

@@ -34,7 +34,8 @@ namespace PepLib.IO
 
             stream.Seek(0x9, SeekOrigin.Current);
 
-            Info.MaterialNumber = int.Parse(ReadString(0x40, ref stream));
+            int.TryParse(ReadString(0x40, ref stream), out var materialNumber);
+            Info.MaterialNumber = materialNumber;
             Info.MaterialGrade = ReadString(0x10, ref stream);
             Info.ProgrammedBy = ReadString(0x40, ref stream);
             Info.CreatedBy = ReadString(0x40, ref stream);