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/Geometry/Shape.cs

@@ -598,6 +598,41 @@ namespace OpenNest.Geometry
             return result;
         }
 
+        /// <summary>
+        /// Offsets the shape inward by the given distance.
+        /// Normalizes to CCW winding before offsetting Left (which is inward for CCW),
+        /// making the method independent of the original contour winding direction.
+        /// </summary>
+        public Shape OffsetInward(double distance)
+        {
+            var poly = ToPolygon();
+
+            if (poly == null || poly.Vertices.Count < 3
+                || poly.RotationDirection() == RotationType.CCW)
+                return OffsetEntity(distance, OffsetSide.Left) as Shape;
+
+            // Create a reversed copy to avoid mutating shared entity objects.
+            var copy = new Shape();
+
+            for (var i = Entities.Count - 1; i >= 0; i--)
+            {
+                switch (Entities[i])
+                {
+                    case Line l:
+                        copy.Entities.Add(new Line(l.EndPoint, l.StartPoint) { Layer = l.Layer });
+                        break;
+                    case Arc a:
+                        copy.Entities.Add(new Arc(a.Center, a.Radius, a.EndAngle, a.StartAngle, !a.IsReversed) { Layer = a.Layer });
+                        break;
+                    case Circle c:
+                        copy.Entities.Add(new Circle(c.Center, c.Radius) { Layer = c.Layer });
+                        break;
+                }
+            }
+
+            return copy.OffsetEntity(distance, OffsetSide.Left) as Shape;
+        }
+
         /// <summary>
         /// Gets the closest point on the shape to the given point.
         /// </summary>