fix: exempt scribe/etch contours from lead-ins and kerf

Scribe/etch lines were being treated as cut contours by
ContourCuttingStrategy, receiving lead-ins and kerf compensation.
Now they are separated before ShapeProfile construction and emitted
as plain moves with LayerType.Scribe preserved.

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

OpenNest/Actions/ActionLeadIn.cs

@@ -249,6 +249,7 @@ namespace OpenNest.Actions
             }
 
             var entities = ConvertProgram.ToGeometry(cleanProgram);
+            entities.RemoveAll(e => e.Layer == SpecialLayers.Scribe);
             profile = new ShapeProfile(entities);
 
             contours = new List<ShapeInfo>();