fix: improve fill progress reporting and engine pipeline

- Strategies now promote results to IsOverallBest when they beat the
  pipeline best, so the UI updates immediately on improvement rather
  than waiting for each phase to complete
- PlateView only updates the main view on overall-best results, fixing
  intermediate angle-sweep layouts leaking to the plate display
- Skip Row/Column strategies for rectangle parts (redundant with Linear)
- Intercept Escape key at MainForm level via ProcessCmdKey so it always
  reaches the active PlateView regardless of focus state
- Restore keyboard focus to PlateView after fill progress form closes
- Remnant engines use SelectBestFitPair for orientation-aware pair
  selection; DefaultNestEngine tries both landscape and portrait pairs
- RemnantFiller preserves more parts during topmost-part removal

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

OpenNest.Engine/HorizontalRemnantEngine.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using OpenNest.Engine;
+using OpenNest.Engine.BestFit;
 using OpenNest.Engine.Fill;
 using OpenNest.Geometry;
 using OpenNest.Math;
@@ -26,6 +27,20 @@ namespace OpenNest
 
         public override ShrinkAxis TrimAxis => ShrinkAxis.Length;
 
+        protected override BestFitResult SelectBestFitPair(List<BestFitResult> results)
+        {
+            BestFitResult best = null;
+
+            foreach (var r in results)
+            {
+                if (!r.Keep) continue;
+                if (best == null || r.BoundingHeight < best.BoundingHeight)
+                    best = r;
+            }
+
+            return best;
+        }
+
         public override List<double> BuildAngles(NestItem item, ClassificationResult classification, Box workArea)
         {
             var baseAngles = new List<double> { classification.PrimaryAngle, classification.PrimaryAngle + Angle.HalfPI };