fix: restore SelectedParts after plate switch in ActionClone

SetPlate clears SelectedParts, which broke bounds drawing and rotation
for surviving actions. Add OnPlateChanged hook so ActionClone can
re-populate SelectedParts after a plate switch.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

OpenNest/Actions/Action.cs

@@ -13,6 +13,8 @@ namespace OpenNest.Actions
 
         public virtual bool SurvivesPlateChange => false;
 
+        public virtual void OnPlateChanged() { }
+
         public abstract void DisconnectEvents();
 
         public abstract void CancelAction();

OpenNest/Actions/ActionClone.cs

@@ -100,6 +100,12 @@ namespace OpenNest.Actions
 
         public override bool SurvivesPlateChange => true;
 
+        public override void OnPlateChanged()
+        {
+            plateView.SelectedParts.Clear();
+            plateView.SelectedParts.AddRange(parts);
+        }
+
         public override void DisconnectEvents()
         {
             plateView.KeyDown -= plateView_KeyDown;

OpenNest/Controls/PlateView.cs

@@ -129,6 +129,8 @@ namespace OpenNest.Controls
 
             if (currentAction == null || !currentAction.SurvivesPlateChange)
                 SetAction(typeof(ActionSelect));
+            else
+                currentAction.OnPlateChanged();
         }
 
         public string Status