feat: add CadImporter.Import stage with bend detection

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

OpenNest.IO/CadImporter.cs

@@ -0,0 +1,49 @@
+using System.Collections.Generic;
+using System.IO;
+using OpenNest.Bending;
+using OpenNest.Geometry;
+using OpenNest.IO.Bending;
+
+namespace OpenNest.IO
+{
+    /// <summary>
+    /// Shared service that converts a CAD source file into a fully-populated
+    /// <see cref="Drawing"/>. Used by the UI, console, MCP, API, and training
+    /// tools so all code paths produce identical drawings.
+    /// </summary>
+    public static class CadImporter
+    {
+        /// <summary>
+        /// Load a DXF file, run bend detection, and return a mutable result
+        /// ready for interactive editing or direct conversion to a Drawing.
+        /// </summary>
+        public static CadImportResult Import(string path, CadImportOptions options = null)
+        {
+            options ??= CadImportOptions.Default;
+
+            var dxf = Dxf.Import(path);
+
+            var bends = new List<Bend>();
+            if (options.DetectBends && dxf.Document != null)
+            {
+                bends = options.BendDetectorName == null
+                    ? BendDetectorRegistry.AutoDetect(dxf.Document)
+                    : BendDetectorRegistry.GetByName(options.BendDetectorName)
+                        ?.DetectBends(dxf.Document)
+                      ?? new List<Bend>();
+            }
+
+            Bend.UpdateEtchEntities(dxf.Entities, bends);
+
+            return new CadImportResult
+            {
+                Entities = dxf.Entities,
+                Bends = bends,
+                Bounds = dxf.Entities.GetBoundingBox(),
+                Document = dxf.Document,
+                SourcePath = path,
+                Name = options.Name ?? Path.GetFileNameWithoutExtension(path),
+            };
+        }
+    }
+}