feat: add CadImporter.Import stage with bend detection

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

OpenNest.Tests/IO/CadImporterTests.cs

@@ -0,0 +1,42 @@
+using System.IO;
+using System.Linq;
+using OpenNest.IO;
+using Xunit;
+
+namespace OpenNest.Tests.IO
+{
+    public class CadImporterTests
+    {
+        private static string TestDxf =>
+            Path.Combine("Bending", "TestData", "4526 A14 PT11.dxf");
+
+        [Fact]
+        public void Import_LoadsEntitiesAndDetectsBends()
+        {
+            var result = CadImporter.Import(TestDxf);
+
+            Assert.NotNull(result);
+            Assert.NotEmpty(result.Entities);
+            Assert.NotNull(result.Bends);
+            Assert.NotNull(result.Bounds);
+            Assert.Equal(TestDxf, result.SourcePath);
+            Assert.Equal("4526 A14 PT11", result.Name);
+        }
+
+        [Fact]
+        public void Import_WhenDetectBendsFalse_ReturnsEmptyBends()
+        {
+            var result = CadImporter.Import(TestDxf, new CadImportOptions { DetectBends = false });
+
+            Assert.Empty(result.Bends);
+        }
+
+        [Fact]
+        public void Import_WhenNameOverrideProvided_UsesOverride()
+        {
+            var result = CadImporter.Import(TestDxf, new CadImportOptions { Name = "custom" });
+
+            Assert.Equal("custom", result.Name);
+        }
+    }
+}