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/DrawingReader.cs

@@ -1,5 +1,4 @@
 using PepLib.Models;
-using System.Diagnostics;
 using System.IO.Compression;
 using System.Text.RegularExpressions;
 
@@ -38,6 +37,11 @@ namespace PepLib.IO
                             LoadInfo(memstream);
                             memstream.Close();
                             continue;
+
+                        case ".loop-info":
+                        case ".cadsnapshot":
+                            memstream.Close();
+                            continue;
                     }
 
                     if (Regex.IsMatch(extension, "loop-\\d\\d\\d"))
@@ -47,6 +51,9 @@ namespace PepLib.IO
                 }
             }
 
+            if (Drawing.Info == null)
+                Drawing.Info = DeriveInfoFromLoops();
+
             Drawing.ResolveLoops();
         }
 
@@ -62,7 +69,7 @@ namespace PepLib.IO
 
             try
             {
-                stream = new FileStream(nestFile, FileMode.Open);
+                stream = new FileStream(nestFile, FileMode.Open, FileAccess.Read, FileShare.Read);
                 Read(stream);
             }
             finally
@@ -74,15 +81,22 @@ namespace PepLib.IO
 
         private void LoadInfo(Stream stream)
         {
-            try
+            Drawing.Info = DrawingInfo.Load(stream);
+        }
+
+        private DrawingInfo DeriveInfoFromLoops()
+        {
+            var info = new DrawingInfo();
+
+            if (Drawing.Loops.Count > 0)
             {
-                Drawing.Info = DrawingInfo.Load(stream);
-            }
-            catch (Exception exception)
-            {
-                Debug.WriteLine(exception.Message);
-                Debug.WriteLine(exception.StackTrace);
+                // Loop names follow the pattern "{DrawingName}.loop-XXX"
+                var loopName = Drawing.Loops[0].Name;
+                var suffix = loopName.LastIndexOf(".loop-", StringComparison.OrdinalIgnoreCase);
+                info.Name = suffix >= 0 ? loopName.Substring(0, suffix) : loopName;
             }
+
+            return info;
         }
 
         private Loop ReadLoop(string name, Stream stream)