feat(core): add RightTriangleShape

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

OpenNest.Core/Shapes/RightTriangleShape.cs

@@ -0,0 +1,23 @@
+using System.Collections.Generic;
+using OpenNest.Geometry;
+
+namespace OpenNest.Shapes
+{
+    public class RightTriangleShape : ShapeDefinition
+    {
+        public double Width { get; set; }
+        public double Height { get; set; }
+
+        public override Drawing GetDrawing()
+        {
+            var entities = new List<Entity>
+            {
+                new Line(0, 0, Width, 0),
+                new Line(Width, 0, 0, Height),
+                new Line(0, Height, 0, 0)
+            };
+
+            return CreateDrawing(entities);
+        }
+    }
+}

OpenNest.Tests/Shapes/RightTriangleShapeTests.cs

@@ -0,0 +1,26 @@
+using OpenNest.Shapes;
+
+namespace OpenNest.Tests.Shapes;
+
+public class RightTriangleShapeTests
+{
+    [Fact]
+    public void GetDrawing_BoundingBoxMatchesDimensions()
+    {
+        var shape = new RightTriangleShape { Width = 12, Height = 8 };
+        var drawing = shape.GetDrawing();
+
+        var bbox = drawing.Program.BoundingBox();
+        Assert.Equal(12, bbox.Width, 0.01);
+        Assert.Equal(8, bbox.Length, 0.01);
+    }
+
+    [Fact]
+    public void GetDrawing_AreaIsHalfWidthTimesHeight()
+    {
+        var shape = new RightTriangleShape { Width = 12, Height = 8 };
+        var drawing = shape.GetDrawing();
+
+        Assert.Equal(48, drawing.Area, 0.5);
+    }
+}