fix: add quantity deduction and progress reporting to StripNestEngine

Nest() now deducts placed counts from input NestItem.Quantity so the
UI loop doesn't create extra plates. All inner DefaultNestEngine.Fill
calls forward the IProgress parameter for live progress updates.

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

OpenNest.Engine/StripNestEngine.cs

@@ -106,18 +106,29 @@ namespace OpenNest
             var remainderItems = items.Where((_, i) => i != stripIndex).ToList();
 
             // Try both orientations.
-            var bottomResult = TryOrientation(StripDirection.Bottom, stripItem, remainderItems, workArea, token);
+            var bottomResult = TryOrientation(StripDirection.Bottom, stripItem, remainderItems, workArea, progress, token);
-            var leftResult = TryOrientation(StripDirection.Left, stripItem, remainderItems, workArea, token);
+            var leftResult = TryOrientation(StripDirection.Left, stripItem, remainderItems, workArea, progress, token);
 
             // Pick the better result.
-            if (bottomResult.Score >= leftResult.Score)
+            var winner = bottomResult.Score >= leftResult.Score
-                return bottomResult.Parts;
+                ? bottomResult.Parts
+                : leftResult.Parts;
 
-            return leftResult.Parts;
+            // Deduct placed quantities from the original items.
+            foreach (var item in items)
+            {
+                if (item.Quantity <= 0)
+                    continue;
+
+                var placed = winner.Count(p => p.BaseDrawing.Name == item.Drawing.Name);
+                item.Quantity = System.Math.Max(0, item.Quantity - placed);
+            }
+
+            return winner;
         }
 
         private StripNestResult TryOrientation(StripDirection direction, NestItem stripItem,
-            List<NestItem> remainderItems, Box workArea, CancellationToken token)
+            List<NestItem> remainderItems, Box workArea, IProgress<NestProgress> progress, CancellationToken token)
         {
             var result = new StripNestResult { Direction = direction };
 
@@ -138,7 +149,7 @@ namespace OpenNest
             var inner = new DefaultNestEngine(Plate);
             var stripParts = inner.Fill(
                 new NestItem { Drawing = stripItem.Drawing, Quantity = stripItem.Quantity },
-                stripBox, null, token);
+                stripBox, progress, token);
 
             if (stripParts == null || stripParts.Count == 0)
                 return result;
@@ -170,7 +181,7 @@ namespace OpenNest
                 var trialInner = new DefaultNestEngine(Plate);
                 var trialParts = trialInner.Fill(
                     new NestItem { Drawing = stripItem.Drawing, Quantity = stripItem.Quantity },
-                    trialBox, null, token);
+                    trialBox, progress, token);
 
                 if (trialParts == null || trialParts.Count < targetCount)
                     break;
@@ -233,7 +244,7 @@ namespace OpenNest
                     var remnantInner = new DefaultNestEngine(Plate);
                     var remnantParts = remnantInner.Fill(
                         new NestItem { Drawing = item.Drawing, Quantity = item.Quantity },
-                        currentRemnant, null, token);
+                        currentRemnant, progress, token);
 
                     if (remnantParts != null && remnantParts.Count > 0)
                     {