fix: 完成本箱后新箱号基于最大箱号递增而非当前箱号

单码装箱和多码凑箱模式统一优化：完成装箱后，下一个箱号
设置为最大箱号+1，避免在查看历史箱号时产生重复箱号。

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

lib/pages/boxing_page.dart

@@ -701,7 +701,7 @@ class _BoxingPageState extends State<BoxingPage> with WidgetsBindingObserver {
         } else {
           setState(() {
             _phase = _Phase.scanned;
-            _boxNoController.text = (boxNo + 1).toString();
+            _boxNoController.text = (_maxBoxNo + 1).toString();
             _quantityController.text = remaining.toString();
             _quantityController.selection = TextSelection(
               baseOffset: 0,
@@ -846,7 +846,6 @@ class _BoxingPageState extends State<BoxingPage> with WidgetsBindingObserver {
   }
 
   void _finishManyToOneBox() {
-    final currentBoxNo = int.tryParse(_boxNoController.text.trim());
     setState(() {
       _manyToOnePackedItems.clear();
       _editingPackedItemId = null;
@@ -855,9 +854,7 @@ class _BoxingPageState extends State<BoxingPage> with WidgetsBindingObserver {
       _zongpaiNo = null;
       _phase = _Phase.waiting;
       _quantityController.clear();
-      if (currentBoxNo != null && currentBoxNo > 0) {
-        _boxNoController.text = (currentBoxNo + 1).toString();
-      }
+      _boxNoController.text = (_maxBoxNo + 1).toString();
       _statusOverrideText = null;
       _statusOverrideDot = null;
     });