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/Controls/PlateView.cs

@@ -584,6 +584,7 @@ namespace OpenNest.Controls
 
                 part.Draw(g, (i + 1).ToString());
                 DrawBendLines(g, part.BasePart);
+                DrawEtchMarks(g, part.BasePart);
                 DrawGrainWarning(g, part.BasePart);
             }
 
@@ -657,6 +658,58 @@ namespace OpenNest.Controls
             }
         }
 
+        private void DrawEtchMarks(Graphics g, Part part)
+        {
+            if (!ShowBendLines || part.BaseDrawing.Bends == null || part.BaseDrawing.Bends.Count == 0)
+                return;
+
+            using var etchPen = new Pen(Color.Green, 1.5f);
+            var etchLength = 1.0;
+
+            foreach (var bend in part.BaseDrawing.Bends)
+            {
+                if (bend.Direction != BendDirection.Up)
+                    continue;
+
+                var start = bend.StartPoint;
+                var end = bend.EndPoint;
+
+                // Apply part rotation
+                if (part.Rotation != 0)
+                {
+                    start = start.Rotate(part.Rotation);
+                    end = end.Rotate(part.Rotation);
+                }
+
+                // Apply part offset
+                start = start + part.Location;
+                end = end + part.Location;
+
+                var length = bend.Length;
+                var angle = bend.StartPoint.AngleTo(bend.EndPoint) + part.Rotation;
+
+                if (length < etchLength * 3.0)
+                {
+                    var pt1 = PointWorldToGraph(start);
+                    var pt2 = PointWorldToGraph(end);
+                    g.DrawLine(etchPen, pt1, pt2);
+                }
+                else
+                {
+                    var dx = System.Math.Cos(angle) * etchLength;
+                    var dy = System.Math.Sin(angle) * etchLength;
+
+                    var s1 = PointWorldToGraph(start);
+                    var e1 = PointWorldToGraph(new Vector(start.X + dx, start.Y + dy));
+                    g.DrawLine(etchPen, s1, e1);
+
+                    var s2 = PointWorldToGraph(end);
+                    var e2 = PointWorldToGraph(new Vector(end.X - dx, end.Y - dy));
+                    g.DrawLine(etchPen, s2, e2);
+                }
+            }
+        }
+
         private void DrawGrainWarning(Graphics g, Part part)
         {
             if (!ShowBendLines || Plate == null || part.BaseDrawing.Bends == null || part.BaseDrawing.Bends.Count == 0)