feat: add lead-out parameters and tab toggle to CuttingParametersForm

Restructure the cutting parameters dialog with separate Lead-In and
Lead-Out GroupBoxes per tab, exposing editable length/angle/radius
fields for lead-outs (previously hardcoded). Add Tabs section with
enable checkbox and width control. Also fix lead-in/lead-out angle
calculations and convert cutting strategy output to incremental mode.

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

OpenNest.Core/CNC/CuttingStrategy/ContourCuttingStrategy.cs

@@ -63,6 +63,10 @@ namespace OpenNest.CNC.CuttingStrategy
                 result.Codes.AddRange(leadOut.Generate(perimeterPt, normal, winding));
             }
 
+            // Convert to incremental mode to match the convention used by
+            // the rest of the system (rendering, bounding box, drag, etc.).
+            result.Mode = Mode.Incremental;
+
             return new CuttingResult
             {
                 Program = result,