fix: normalize best-fit pairs to landscape and fix viewer size swap

Normalize pair bounding box to landscape (width >= height) in
PairEvaluator for consistent display and filtering. Fix
BestFitViewerForm where BoundingWidth/BoundingHeight were passed
in the wrong order to the plate Size constructor.

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

OpenNest.Engine/BestFit/PairEvaluator.cs

@@ -1,6 +1,7 @@
 using OpenNest.Converters;
 using OpenNest.Engine.Fill;
 using OpenNest.Geometry;
+using OpenNest.Math;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Linq;
@@ -67,6 +68,15 @@ namespace OpenNest.Engine.BestFit
 
             var trueArea = drawing.Area * 2;
 
+            // Normalize to landscape (width >= height) for consistent display.
+            if (bestHeight > bestWidth)
+            {
+                var tmp = bestWidth;
+                bestWidth = bestHeight;
+                bestHeight = tmp;
+                bestRotation += Angle.HalfPI;
+            }
+
             return new BestFitResult
             {
                 Candidate = candidate,