fix: swap bounding box dimensions in BestFitViewerForm

Size(width, length) maps Width to vertical and Length to horizontal in
PlateView, but BoundingWidth (the longer dimension) was being passed as
Width (vertical) instead of Length (horizontal), causing the bounding
box to appear portrait instead of landscape.

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

OpenNest/Forms/BestFitViewerForm.cs

@@ -291,8 +291,8 @@ namespace OpenNest.Forms
             cell.PartColor = partColor;
             cell.Dock = DockStyle.Fill;
             cell.Plate.Size = new Geometry.Size(
-                result.BoundingWidth,
-                result.BoundingHeight);
+                result.BoundingHeight,
+                result.BoundingWidth);
 
             var parts = result.BuildParts(drawing);