feat: add pierce point visualization and rename shape dimensions to Length/Width

Add toggleable pierce point drawing to PlateView that shows small red
filled circles at each rapid move endpoint (where cutting begins). Wire
through View menu, EditNestForm toggle, and MainForm handler.

Also rename RectangleShape/RoundedRectangleShape Width/Height to
Length/Width for consistency with CNC conventions, update MCP tools and
tests accordingly. Fix SplitDrawingForm designer layout ordering and
EntityView bend line selection styling.

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

OpenNest/Forms/EditNestForm.cs

@@ -473,6 +473,12 @@ namespace OpenNest.Forms
             PlateView.Invalidate();
         }
 
+        public void TogglePiercePoints()
+        {
+            PlateView.DrawPiercePoints = !PlateView.DrawPiercePoints;
+            PlateView.Invalidate();
+        }
+
         public void ToggleDrawBounds()
         {
             PlateView.DrawBounds = !PlateView.DrawBounds;