refactor: organize test project into subdirectories by feature area

Move 43 root-level test files into feature-specific subdirectories
mirroring the main codebase structure: Geometry, Fill, BestFit, CutOffs,
CuttingStrategy, Engine, IO. Update namespaces to match folder paths.

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

OpenNest.Tests/Geometry/PolyLabelTests.cs

@@ -0,0 +1,129 @@
+using OpenNest.Geometry;
+
+namespace OpenNest.Tests.Geometry;
+
+public class PolyLabelTests
+{
+    private static Polygon Square(double size)
+    {
+        var p = new Polygon();
+        p.Vertices.Add(new Vector(0, 0));
+        p.Vertices.Add(new Vector(size, 0));
+        p.Vertices.Add(new Vector(size, size));
+        p.Vertices.Add(new Vector(0, size));
+        return p;
+    }
+
+    [Fact]
+    public void Square_ReturnsCenterPoint()
+    {
+        var poly = Square(100);
+
+        var result = PolyLabel.Find(poly);
+
+        Assert.Equal(50, result.X, 1.0);
+        Assert.Equal(50, result.Y, 1.0);
+    }
+
+    [Fact]
+    public void Triangle_ReturnsIncenter()
+    {
+        var p = new Polygon();
+        p.Vertices.Add(new Vector(0, 0));
+        p.Vertices.Add(new Vector(100, 0));
+        p.Vertices.Add(new Vector(50, 86.6));
+
+        var result = PolyLabel.Find(p);
+
+        // Incenter of equilateral triangle is at (50, ~28.9)
+        Assert.Equal(50, result.X, 1.0);
+        Assert.Equal(28.9, result.Y, 1.0);
+        Assert.True(p.ContainsPoint(result));
+    }
+
+    [Fact]
+    public void LShape_ReturnsPointInBottomLobe()
+    {
+        // L-shape: 100x100 with 50x50 cut from top-right
+        var p = new Polygon();
+        p.Vertices.Add(new Vector(0, 0));
+        p.Vertices.Add(new Vector(100, 0));
+        p.Vertices.Add(new Vector(100, 50));
+        p.Vertices.Add(new Vector(50, 50));
+        p.Vertices.Add(new Vector(50, 100));
+        p.Vertices.Add(new Vector(0, 100));
+
+        var result = PolyLabel.Find(p);
+
+        Assert.True(p.ContainsPoint(result));
+        // The bottom 100x50 lobe is the widest region
+        Assert.True(result.Y < 50, $"Expected label in bottom lobe, got Y={result.Y}");
+    }
+
+    [Fact]
+    public void ThinRectangle_CenteredOnBothAxes()
+    {
+        var p = new Polygon();
+        p.Vertices.Add(new Vector(0, 0));
+        p.Vertices.Add(new Vector(200, 0));
+        p.Vertices.Add(new Vector(200, 10));
+        p.Vertices.Add(new Vector(0, 10));
+
+        var result = PolyLabel.Find(p);
+
+        Assert.Equal(100, result.X, 1.0);
+        Assert.Equal(5, result.Y, 1.0);
+        Assert.True(p.ContainsPoint(result));
+    }
+
+    [Fact]
+    public void SquareWithLargeHole_AvoidsHole()
+    {
+        var outer = Square(100);
+
+        var hole = new Polygon();
+        hole.Vertices.Add(new Vector(20, 20));
+        hole.Vertices.Add(new Vector(80, 20));
+        hole.Vertices.Add(new Vector(80, 80));
+        hole.Vertices.Add(new Vector(20, 80));
+
+        var result = PolyLabel.Find(outer, new[] { hole });
+
+        // Point should be inside outer but outside hole
+        Assert.True(outer.ContainsPoint(result));
+        Assert.False(hole.ContainsPoint(result));
+    }
+
+    [Fact]
+    public void CShape_ReturnsPointInLeftBar()
+    {
+        // C-shape opening to the right: left bar is 20 wide, top/bottom arms are 20 tall
+        var p = new Polygon();
+        p.Vertices.Add(new Vector(0, 0));
+        p.Vertices.Add(new Vector(100, 0));
+        p.Vertices.Add(new Vector(100, 20));
+        p.Vertices.Add(new Vector(20, 20));
+        p.Vertices.Add(new Vector(20, 80));
+        p.Vertices.Add(new Vector(100, 80));
+        p.Vertices.Add(new Vector(100, 100));
+        p.Vertices.Add(new Vector(0, 100));
+
+        var result = PolyLabel.Find(p);
+
+        Assert.True(p.ContainsPoint(result));
+        // Label should be in the left vertical bar (x < 20), not at bbox center (50, 50)
+        Assert.True(result.X < 20, $"Expected label in left bar, got X={result.X}");
+    }
+
+    [Fact]
+    public void DegeneratePolygon_ReturnsFallback()
+    {
+        var p = new Polygon();
+        p.Vertices.Add(new Vector(5, 5));
+
+        var result = PolyLabel.Find(p);
+
+        Assert.Equal(5, result.X, 0.01);
+        Assert.Equal(5, result.Y, 0.01);
+    }
+}