fix: preserve bend lines through drawing split — clip, offset, and carry metadata

DrawingSplitter now clips bend lines to each piece's region using
Liang-Barsky line clipping and offsets them to the new origin. Bend
properties (direction, angle, radius, note text) are preserved through
the entire split pipeline instead of being lost during re-import.

CadConverterForm applies the same origin offset to bends before passing
them to the splitter, and creates FileListItems directly from split
results to avoid re-detection overwriting the bend metadata.

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

OpenNest.Tests/Bending/SolidWorksBendDetectorTests.cs

@@ -1,3 +1,4 @@
+using ACadSharp.IO;
 using OpenNest.Bending;
 using OpenNest.IO.Bending;
 
@@ -27,4 +28,27 @@ public class SolidWorksBendDetectorTests
         var bends = BendDetectorRegistry.AutoDetect(doc);
         Assert.Empty(bends);
     }
+
+    [Fact]
+    public void DetectBends_RealDxf_ParsesNotesCorrectly()
+    {
+        var path = Path.Combine(AppContext.BaseDirectory, "Bending", "TestData", "4526 A14 PT45.dxf");
+        Assert.True(File.Exists(path), $"Test DXF not found: {path}");
+
+        using var reader = new DxfReader(path);
+        var doc = reader.Read();
+
+        var detector = new SolidWorksBendDetector();
+        var bends = detector.DetectBends(doc);
+
+        Assert.Equal(2, bends.Count);
+
+        foreach (var bend in bends)
+        {
+            Assert.NotNull(bend.NoteText);
+            Assert.Equal(BendDirection.Up, bend.Direction);
+            Assert.Equal(90.0, bend.Angle);
+            Assert.Equal(0.313, bend.Radius);
+        }
+    }
 }

OpenNest.Tests/OpenNest.Tests.csproj

@@ -28,4 +28,10 @@
     <ProjectReference Include="..\OpenNest.Posts.Cincinnati\OpenNest.Posts.Cincinnati.csproj" />
   </ItemGroup>
 
+  <ItemGroup>
+    <Content Include="Bending\TestData\**\*">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </Content>
+  </ItemGroup>
+
 </Project>