fix: draw approach rapid directly to first pierce point, not part origin

The approach rapid from sheet origin was drawing to part.Location (the
program coordinate origin) then a second rapid to the actual first
pierce point. This created a dog-leg through the part origin instead
of a single straight rapid to the lead-in. Also fixed PlateProcessor
using the original program's start point instead of the processed one
when the cutting strategy is applied on-the-fly.

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

OpenNest.Engine/PlateProcessor.cs

@@ -44,7 +44,7 @@ namespace OpenNest.Engine
                 }
 
                 // Pierce point: program start point in plate space
-                var pierceLocal = GetProgramStartPoint(part.Program);
+                var pierceLocal = GetProgramStartPoint(processedProgram);
                 var piercePoint = ToPlateSpace(pierceLocal, part);
 
                 // Plan rapid from currentPoint to pierce point