feat(core): add FlangeShape with JSON preset loading

FlangeShape generates an outer circle with evenly-spaced bolt holes
on a bolt circle pattern. ShapeDefinition.LoadFromJson<T>() provides
generic JSON loading for any shape — no separate preset classes needed.

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

OpenNest.Core/Shapes/FlangeShape.cs

@@ -0,0 +1,38 @@
+using System;
+using System.Collections.Generic;
+using OpenNest.Geometry;
+
+namespace OpenNest.Shapes
+{
+    public class FlangeShape : ShapeDefinition
+    {
+        public double NominalPipeSize { get; set; }
+        public double OD { get; set; }
+        public double HoleDiameter { get; set; }
+        public double HolePatternDiameter { get; set; }
+        public int HoleCount { get; set; }
+
+        public override Drawing GetDrawing()
+        {
+            var entities = new List<Entity>();
+
+            // Outer circle
+            entities.Add(new Circle(0, 0, OD / 2.0));
+
+            // Bolt holes evenly spaced on the bolt circle
+            var boltCircleRadius = HolePatternDiameter / 2.0;
+            var holeRadius = HoleDiameter / 2.0;
+            var angleStep = 2.0 * System.Math.PI / HoleCount;
+
+            for (var i = 0; i < HoleCount; i++)
+            {
+                var angle = i * angleStep;
+                var cx = boltCircleRadius * System.Math.Cos(angle);
+                var cy = boltCircleRadius * System.Math.Sin(angle);
+                entities.Add(new Circle(cx, cy, holeRadius));
+            }
+
+            return CreateDrawing(entities);
+        }
+    }
+}

OpenNest.Core/Shapes/ShapeDefinition.cs

@@ -1,5 +1,7 @@
 using System;
 using System.Collections.Generic;
+using System.IO;
+using System.Text.Json;
 using OpenNest.Converters;
 using OpenNest.Geometry;
 
@@ -7,6 +9,11 @@ namespace OpenNest.Shapes
 {
     public abstract class ShapeDefinition
     {
+        private static readonly JsonSerializerOptions JsonOptions = new JsonSerializerOptions
+        {
+            PropertyNameCaseInsensitive = true
+        };
+
         public string Name { get; set; }
 
         protected ShapeDefinition()
@@ -19,6 +26,12 @@ namespace OpenNest.Shapes
 
         public abstract Drawing GetDrawing();
 
+        public static List<T> LoadFromJson<T>(string path) where T : ShapeDefinition
+        {
+            var json = File.ReadAllText(path);
+            return JsonSerializer.Deserialize<List<T>>(json, JsonOptions);
+        }
+
         protected Drawing CreateDrawing(List<Entity> entities)
         {
             var pgm = ConvertGeometry.ToProgram(entities);

OpenNest.Tests/Shapes/FlangeShapeTests.cs

@@ -0,0 +1,105 @@
+using OpenNest.CNC;
+using OpenNest.Shapes;
+
+namespace OpenNest.Tests.Shapes;
+
+public class FlangeShapeTests
+{
+    [Fact]
+    public void GetDrawing_BoundingBoxMatchesOD()
+    {
+        var shape = new FlangeShape
+        {
+            OD = 10,
+            HoleDiameter = 1,
+            HolePatternDiameter = 7,
+            HoleCount = 4
+        };
+        var drawing = shape.GetDrawing();
+
+        var bbox = drawing.Program.BoundingBox();
+        Assert.Equal(10, bbox.Width, 0.01);
+        Assert.Equal(10, bbox.Length, 0.01);
+    }
+
+    [Fact]
+    public void GetDrawing_AreaExcludesBoltHoles()
+    {
+        var shape = new FlangeShape
+        {
+            OD = 10,
+            HoleDiameter = 1,
+            HolePatternDiameter = 7,
+            HoleCount = 4
+        };
+        var drawing = shape.GetDrawing();
+
+        // Area = pi * 5^2 - 4 * pi * 0.5^2 = pi * (25 - 1) = pi * 24
+        var expectedArea = System.Math.PI * 24;
+        Assert.Equal(expectedArea, drawing.Area, 0.5);
+    }
+
+    [Fact]
+    public void GetDrawing_DefaultName_IsFlange()
+    {
+        var shape = new FlangeShape
+        {
+            OD = 10,
+            HoleDiameter = 1,
+            HolePatternDiameter = 7,
+            HoleCount = 4
+        };
+        var drawing = shape.GetDrawing();
+
+        Assert.Equal("Flange", drawing.Name);
+    }
+
+    [Fact]
+    public void LoadFromJson_ProducesCorrectDrawing()
+    {
+        var json = """
+        [
+          {
+            "Name": "2in-150#",
+            "NominalPipeSize": 2.0,
+            "OD": 6.0,
+            "HoleDiameter": 0.75,
+            "HolePatternDiameter": 4.75,
+            "HoleCount": 4
+          },
+          {
+            "Name": "2in-300#",
+            "NominalPipeSize": 2.0,
+            "OD": 6.5,
+            "HoleDiameter": 0.75,
+            "HolePatternDiameter": 5.0,
+            "HoleCount": 8
+          }
+        ]
+        """;
+
+        var tempFile = Path.GetTempFileName();
+        try
+        {
+            File.WriteAllText(tempFile, json);
+
+            var flanges = ShapeDefinition.LoadFromJson<FlangeShape>(tempFile);
+
+            Assert.Equal(2, flanges.Count);
+
+            var first = flanges[0];
+            Assert.Equal("2in-150#", first.Name);
+            var drawing = first.GetDrawing();
+            var bbox = drawing.Program.BoundingBox();
+            Assert.Equal(6, bbox.Width, 0.01);
+
+            var second = flanges[1];
+            Assert.Equal("2in-300#", second.Name);
+            Assert.Equal(8, second.HoleCount);
+        }
+        finally
+        {
+            File.Delete(tempFile);
+        }
+    }
+}