feat: add etch mark entities from bend lines to CNC program pipeline

Etch marks for up bends are now real geometry entities on an ETCH layer
instead of being drawn dynamically. They flow through the full pipeline:
entities → FilterPanel layers → ConvertGeometry (tagged as Scribe) →
post-processor sequencing before cut geometry.

Also includes ShapeProfile normalization (CW perimeter, CCW cutouts)
applied consistently across all import paths, and inward offset support
for cutout shapes in overlap/offset polygon calculations.

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

OpenNest.Core/Converters/ConvertGeometry.cs

@@ -108,7 +108,10 @@ namespace OpenNest.Converters
             if (line.StartPoint != lastpt)
                 pgm.MoveTo(line.StartPoint);
 
-            pgm.LineTo(line.EndPoint);
+            var move = new LinearMove(line.EndPoint);
+            if (string.Equals(line.Layer?.Name, "ETCH", System.StringComparison.OrdinalIgnoreCase))
+                move.Layer = LayerType.Scribe;
+            pgm.Codes.Add(move);
 
             lastpt = line.EndPoint;
             return lastpt;