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.IO/Bending/SolidWorksBendDetector.cs

@@ -17,9 +17,13 @@ namespace OpenNest.IO.Bending
         public double MaxBendRadius { get; set; } = 4.0;
 
         private static readonly Regex BendNoteRegex = new Regex(
-            @"\b(?<direction>UP|DOWN|DN)\s+(?<angle>\d+(\.\d+)?)°?\s*R\s*(?<radius>\d+(\.\d+)?)\b",
+            @"(?<direction>UP|DOWN|DN)\s+(?<angle>\d+(\.\d+)?)[^A-Z\d]*R\s*(?<radius>\d+(\.\d+)?)",
             RegexOptions.Compiled | RegexOptions.IgnoreCase);
 
+        private static readonly Regex MTextFormatRegex = new Regex(
+            @"\\[fHCTQWASpOoLlKk][^;]*;|\\P|[{}]|%%[dDpPcC]",
+            RegexOptions.Compiled);
+
         public List<Bend> DetectBends(CadDocument document)
         {
             var bendLines = FindBendLines(document);
@@ -45,9 +49,10 @@ namespace OpenNest.IO.Bending
                 var note = FindClosestBendNote(line, bendNotes);
                 if (note != null)
                 {
-                    bend.Direction = GetBendDirection(note.Value);
-                    bend.NoteText = note.Value;
-                    ParseBendNote(note.Value, bend);
+                    var noteText = StripMTextFormatting(note.Value);
+                    bend.Direction = GetBendDirection(noteText);
+                    bend.NoteText = noteText;
+                    ParseBendNote(noteText, bend);
                 }
 
                 if (!bend.Radius.HasValue || bend.Radius.Value <= MaxBendRadius)
@@ -106,6 +111,24 @@ namespace OpenNest.IO.Bending
             }
         }
 
+        private static string StripMTextFormatting(string text)
+        {
+            if (string.IsNullOrEmpty(text))
+                return text;
+
+            // Replace known DXF special characters
+            var result = text
+                .Replace("%%d", "°").Replace("%%D", "°")
+                .Replace("%%p", "±").Replace("%%P", "±")
+                .Replace("%%c", "⌀").Replace("%%C", "⌀");
+
+            // Strip MText formatting codes and braces
+            result = MTextFormatRegex.Replace(result, " ");
+
+            // Collapse multiple spaces
+            return Regex.Replace(result.Trim(), @"\s+", " ");
+        }
+
         private MText FindClosestBendNote(ACadSharp.Entities.Line bendLine, List<MText> notes)
         {
             if (notes.Count == 0) return null;