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/Utilities/ZipHelper.cs

@@ -18,7 +18,7 @@ namespace PepLib.Utilities
             var nameList = new List<string>();
             var streamList = new List<Stream>();
 
-            using (var fileStream = new FileStream(file, FileMode.Open, FileAccess.Read))
+            using (var fileStream = new FileStream(file, FileMode.Open, FileAccess.Read, FileShare.Read))
             using (var zip = new ZipArchive(fileStream, ZipArchiveMode.Read))
             {
                 foreach (var entry in zip.Entries)
@@ -52,7 +52,7 @@ namespace PepLib.Utilities
         /// <returns></returns>
         public static bool ExtractByExtension(string file, string extension, out string name, out Stream stream)
         {
-            using (var fileStream = new FileStream(file, FileMode.Open, FileAccess.Read))
+            using (var fileStream = new FileStream(file, FileMode.Open, FileAccess.Read, FileShare.Read))
             using (var zip = new ZipArchive(fileStream, ZipArchiveMode.Read))
             {
                 foreach (var entry in zip.Entries)