fix: assign colors to SpecialLayers and ConvertProgram entities

ConvertProgram.ToGeometry() created entities without setting Color,
defaulting to Color.Empty (alpha=0). After ededc7b switched from
Pens.White to per-entity colors, these rendered fully transparent.

- Add explicit colors to all SpecialLayers (Cut=White, Rapid=Gray, etc.)
- Set entity Color from layer in ConvertProgram for lines, arcs, circles
- Add GetEntityPen fallback: treat Empty/alpha-0 as White
- Add bend line rendering and selection in EntityView/CadConverterForm
- Fix SolidWorksBendDetector MText formatting strip for bend notes

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

OpenNest/Controls/EntityView.cs

@@ -1,4 +1,5 @@
-using OpenNest.Geometry;
+using OpenNest.Bending;
+using OpenNest.Geometry;
 using OpenNest.Math;
 using System.Collections.Generic;
 using System.Drawing;
@@ -10,6 +11,8 @@ namespace OpenNest.Controls
     public class EntityView : DrawControl
     {
         public List<Entity> Entities;
+        public List<Bend> Bends = new List<Bend>();
+        public int SelectedBendIndex = -1;
 
         private readonly Pen gridPen = new Pen(Color.FromArgb(70, 70, 70));
         private readonly Dictionary<int, Pen> penCache = new Dictionary<int, Pen>();
@@ -49,6 +52,8 @@ namespace OpenNest.Controls
                 DrawEntity(e.Graphics, entity, pen);
             }
 
+            DrawBendLines(e.Graphics);
+
 #if DRAW_OFFSET
 
             var offsetShape = new Shape();
@@ -106,6 +111,9 @@ namespace OpenNest.Controls
 
         private Pen GetEntityPen(Color color)
         {
+            if (color.IsEmpty || color.A == 0)
+                color = Color.White;
+
             // Clamp dark colors to ensure visibility on dark background
             var brightness = (color.R * 299 + color.G * 587 + color.B * 114) / 1000;
             if (brightness < 80)
@@ -130,6 +138,29 @@ namespace OpenNest.Controls
             penCache.Clear();
         }
 
+        private void DrawBendLines(Graphics g)
+        {
+            if (Bends == null || Bends.Count == 0)
+                return;
+
+            using var bendPen = new Pen(Color.Yellow, 1.5f)
+            {
+                DashStyle = DashStyle.Dash
+            };
+            using var selectedPen = new Pen(Color.Cyan, 2.5f)
+            {
+                DashStyle = DashStyle.Dash
+            };
+
+            for (var i = 0; i < Bends.Count; i++)
+            {
+                var bend = Bends[i];
+                var pt1 = PointWorldToGraph(bend.StartPoint);
+                var pt2 = PointWorldToGraph(bend.EndPoint);
+                g.DrawLine(i == SelectedBendIndex ? selectedPen : bendPen, pt1, pt2);
+            }
+        }
+
         protected override void Dispose(bool disposing)
         {
             if (disposing)

OpenNest/Forms/CadConverterForm.cs

@@ -134,6 +134,7 @@ namespace OpenNest.Forms
             entityView1.ClearPenCache();
             entityView1.Entities.Clear();
             entityView1.Entities.AddRange(item.Entities);
+            entityView1.Bends = item.Bends ?? new List<Bend>();
 
             item.Entities.ForEach(e => e.IsVisible = true);
             if (item.Entities.Any(e => e.Layer != null))
@@ -174,7 +175,7 @@ namespace OpenNest.Forms
 
         private void OnBendLineSelected(object sender, int index)
         {
-            // TODO: Highlight bend line in EntityView
+            entityView1.SelectedBendIndex = index;
             entityView1.Invalidate();
         }
 
@@ -184,6 +185,8 @@ namespace OpenNest.Forms
             if (item == null || index < 0 || index >= item.Bends.Count) return;
 
             item.Bends.RemoveAt(index);
+            entityView1.Bends = item.Bends;
+            entityView1.SelectedBendIndex = -1;
             filterPanel.LoadItem(item.Entities, item.Bends);
             entityView1.Invalidate();
         }