feat: add Tab hierarchy (4 classes)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

OpenNest.Core/CNC/CuttingStrategy/Tabs/Tab.cs

@@ -0,0 +1,16 @@
+using System.Collections.Generic;
+using OpenNest.Geometry;
+
+namespace OpenNest.CNC.CuttingStrategy
+{
+    public abstract class Tab
+    {
+        public double Size { get; set; } = 0.03;
+        public LeadIn TabLeadIn { get; set; }
+        public LeadOut TabLeadOut { get; set; }
+
+        public abstract List<ICode> Generate(
+            Vector tabStartPoint, Vector tabEndPoint, double contourNormalAngle,
+            RotationType winding = RotationType.CW);
+    }
+}