feat(desktop): draw cut-off lines as a prominent orange-red dash

Cut-off scrap lines were a solid 1.5px near-black stroke that read like
another sheet/part outline. They now render as a 2px orange-red dash so
operators can spot scrap cuts at a glance, and the manual cut-off preview
is recolored to match the applied line. Selected cut-offs keep their solid
blue highlight.

Add bitmap regression tests (CutOffDisplayTests) that verify the dashed
orange style, the dashed gaps, and the unchanged selection highlight.

OpenNest.WinForms.Tests/CutOffDisplayTests.cs

@@ -0,0 +1,98 @@
+using System.Drawing;
+using System.Drawing.Drawing2D;
+using OpenNest.Controls;
+using OpenNest.Geometry;
+
+namespace OpenNest.WinForms.Tests;
+
+public class CutOffDisplayTests
+{
+    private static readonly Color OldLineGray = Color.FromArgb(64, 64, 64);
+    private static readonly Color CutoffLine = Color.OrangeRed;
+    private static readonly Color SelectedBlue = Color.FromArgb(0, 120, 255);
+
+    // A 100x100 quadrant-4 sheet puts a vertical cut-off at x=50 on the
+    // graph column x=50, rows 0..100 (PointWorldToGraph flips Y).
+    private static (PlateView View, CutOff Cutoff) BuildPlateWithCutOff()
+    {
+        var view = new PlateView(ColorSchemeRegistry.Get("Workshop"))
+        {
+            Size = new System.Drawing.Size(100, 100),
+        };
+        view.Matrix = new Matrix();
+        view.Plate.Size = new OpenNest.Geometry.Size(100, 100);
+        view.Plate.Quadrant = 4;
+        var cutoff = new CutOff(new Vector(50, 0), CutOffAxis.Vertical);
+        view.Plate.CutOffs.Add(cutoff);
+        view.Plate.RegenerateCutOffs(new CutOffSettings());
+        return (view, cutoff);
+    }
+
+    private static (int Orange, int White, int OldGray, int Blue) CountLinePixels(Bitmap image)
+    {
+        var orange = 0;
+        var white = 0;
+        var oldGray = 0;
+        var blue = 0;
+
+        for (var y = 3; y <= 96; y++)
+        {
+            for (var x = 48; x <= 52; x++)
+            {
+                var c = image.GetPixel(x, y);
+
+                if (c.R >= 200 && c.G <= 120 && c.B <= 80)
+                    orange++;
+                else if (c.R >= 240 && c.G >= 240 && c.B >= 240)
+                    white++;
+                else if (
+                    System.Math.Abs(c.R - OldLineGray.R) <= 32
+                    && System.Math.Abs(c.G - OldLineGray.G) <= 32
+                    && System.Math.Abs(c.B - OldLineGray.B) <= 32
+                )
+                    oldGray++;
+                else if (c.B >= 200 && c.R <= 60)
+                    blue++;
+            }
+        }
+
+        return (orange, white, oldGray, blue);
+    }
+
+    [Fact]
+    public void CutOffLineIsDashedOrangeNotSolidBlack() => StaTestThread.Run(() =>
+    {
+        var (view, _) = BuildPlateWithCutOff();
+        using (view)
+        using (var image = new Bitmap(100, 100))
+        using (var g = Graphics.FromImage(image))
+        {
+            g.Clear(Color.White);
+            view.Renderer.DrawCutOffs(g);
+
+            var (orange, white, oldGray, _) = CountLinePixels(image);
+            Assert.True(orange >= 10, $"Expected the orange cut-off dash, found {orange} pixels.");
+            Assert.True(white >= 10, $"Expected dashed gaps along the cut-off line, found {white} white pixels.");
+            Assert.Equal(0, oldGray);
+        }
+    }, TimeSpan.FromMinutes(1), "Cut-off display test timed out.");
+
+    [Fact]
+    public void SelectedCutOffKeepsSolidBlueHighlight() => StaTestThread.Run(() =>
+    {
+        var (view, cutoff) = BuildPlateWithCutOff();
+        using (view)
+        {
+            view.Selection.SelectedCutOffs.Add(cutoff);
+            using var image = new Bitmap(100, 100);
+            using var g = Graphics.FromImage(image);
+            g.Clear(Color.White);
+            view.Renderer.DrawCutOffs(g);
+
+            var (orange, _, oldGray, blue) = CountLinePixels(image);
+            Assert.True(blue >= 20, $"Expected the solid blue selection line, found {blue} pixels.");
+            Assert.Equal(0, orange);
+            Assert.Equal(0, oldGray);
+        }
+    }, TimeSpan.FromMinutes(1), "Selected cut-off display test timed out.");
+}

OpenNest/Actions/ActionCutOff.cs

@@ -100,7 +100,10 @@ namespace OpenNest.Actions
             if (program.Codes.Count == 0)
                 return;
 
-            using var pen = new Pen(Color.FromArgb(128, 64, 64, 64), 1.5f / plateView.ViewScale)
+            // Match the applied cut-off line's look (orange-red dash) so the
+            // preview is exactly what the click produces; the alpha keeps it
+            // reading as a preview.
+            using var pen = new Pen(Color.FromArgb(128, 255, 69, 0), 1.5f / plateView.ViewScale)
             {
                 DashStyle = DashStyle.Dash,
             };

OpenNest/Controls/PlateRenderer.cs

@@ -242,13 +242,17 @@ namespace OpenNest.Controls
             }
         }
 
+        // Scrap cut-off lines must stand out from the dark part outlines and the
+        // sheet: a saturated orange-red dash, not another solid near-black line.
+        private static readonly Color CutOffLineColor = Color.OrangeRed;
+
         public void DrawCutOffs(Graphics g)
         {
             var plate = view.DisplayPlate;
             if (plate?.CutOffs == null || plate.CutOffs.Count == 0)
                 return;
 
-            using var pen = new Pen(Color.FromArgb(64, 64, 64), 1.5f);
+            using var pen = new Pen(CutOffLineColor, 2.0f) { DashStyle = DashStyle.Dash };
             using var selectedPen = new Pen(Color.FromArgb(0, 120, 255), 3.5f);
 
             foreach (var cutoff in plate.CutOffs)