fix(ui): use LeastCode sequencer and fix AddRange double-enumeration

Advanced sequencer with default 0.25 MinDistanceBetweenRowsColumns
puts every part in its own row, degenerating to a Y-sort. Switch to
LeastCode (nearest-neighbor + 2-opt) for visible results.

Also replace AddRange(linq) with foreach+Add to avoid ObservableList
AddRange re-enumerating a deferred LINQ query for event firing.

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

OpenNest/Forms/EditNestForm.cs

@@ -456,12 +456,13 @@ namespace OpenNest.Forms
 
         private static void SequencePlate(Plate plate)
         {
-            var parameters = new SequenceParameters();
+            var parameters = new SequenceParameters { Method = SequenceMethod.LeastCode };
             var sequencer = PartSequencerFactory.Create(parameters);
             var ordered = sequencer.Sequence(plate.Parts.ToList(), plate);
 
             plate.Parts.Clear();
-            plate.Parts.AddRange(ordered.Select(s => s.Part));
+            foreach (var s in ordered)
+                plate.Parts.Add(s.Part);
         }
 
         public void CalculateCurrentPlateCutTime()