feat: add CutOff and CutOffSettings domain classes with segment generation

CutOff computes cut segments along a vertical or horizontal axis,
excluding zones around existing parts with configurable clearance.
CutOffSettings controls part clearance, overtravel, minimum segment
length, and cut direction (toward/away from origin).

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

OpenNest.Core/CutOffSettings.cs

@@ -0,0 +1,16 @@
+namespace OpenNest
+{
+    public enum CutDirection
+    {
+        TowardOrigin,
+        AwayFromOrigin
+    }
+
+    public class CutOffSettings
+    {
+        public double PartClearance { get; set; } = 0.125;
+        public double Overtravel { get; set; }
+        public double MinSegmentLength { get; set; } = 0.05;
+        public CutDirection CutDirection { get; set; } = CutDirection.TowardOrigin;
+    }
+}