feat: add material library resolution, assist gas support, and UI fixes

- Add MaterialLibraryResolver for Cincinnati post processor to resolve
  G89 library files from material/thickness/gas configuration
- Add Nest.AssistGas property with serialization support in nest format
- Add etch library support with separate gas configuration
- Fix CutOff tests to match AwayFromOrigin default cut direction
- Fix plate info label not updating after ResizePlateToFitParts
- Add cutoff and remnants toolbar button icons

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

OpenNest/Forms/EditNestForm.cs

@@ -458,6 +458,7 @@ namespace OpenNest.Forms
             PlateView.ZoomToPlate();
             PlateView.Refresh();
             UpdatePlateList();
+            UpdatePlateHeader();
         }
 
         public void SelectAllParts()