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/Strategies/ColumnFillStrategy.cs

@@ -11,6 +11,9 @@ public class ColumnFillStrategy : IFillStrategy
 
     public List<Part> Fill(FillContext context)
     {
+        if (context.PartType == PartType.Rectangle)
+            return null;
+
         var filler = new StripeFiller(context, NestDirection.Vertical) { CompleteStripesOnly = true };
         return filler.Fill();
     }

OpenNest.Engine/Strategies/FillContext.cs

@@ -32,16 +32,29 @@ namespace OpenNest.Engine.Strategies
         /// <summary>
         /// Standard progress reporting for strategies and fillers. Reports intermediate
         /// results using the current ActivePhase, PlateNumber, and WorkArea.
+        /// When the reported parts beat the current pipeline best, promotes the
+        /// result to IsOverallBest so the UI updates immediately.
         /// </summary>
         public void ReportProgress(List<Part> parts, string description)
         {
+            var isNewBest = parts != null && parts.Count > 0
+                && Policy.Comparer.IsBetter(parts, CurrentBest, WorkArea);
+
+            if (isNewBest)
+            {
+                CurrentBest = parts;
+                CurrentBestScore = FillScore.Compute(parts, WorkArea);
+                WinnerPhase = ActivePhase;
+            }
+
             NestEngineBase.ReportProgress(Progress, new ProgressReport
             {
                 Phase = ActivePhase,
                 PlateNumber = PlateNumber,
-                Parts = parts,
+                Parts = isNewBest ? parts : CurrentBest,
                 WorkArea = WorkArea,
                 Description = description,
+                IsOverallBest = isNewBest,
             });
         }
     }

OpenNest.Engine/Strategies/RowFillStrategy.cs

@@ -11,6 +11,9 @@ public class RowFillStrategy : IFillStrategy
 
     public List<Part> Fill(FillContext context)
     {
+        if (context.PartType == PartType.Rectangle)
+            return null;
+
         var filler = new StripeFiller(context, NestDirection.Horizontal) { CompleteStripesOnly = true };
         return filler.Fill();
     }