feat: extend boxing page for accessory boxing support

Add pending accessories section to both single-code and multi-code boxing
modes. Accessories display with orange styling and a "加入本箱" button that
calls saveBoxRecord with item_type=accessory. Extend API service with
PendingAccessory model, itemType fields on data classes, and optional
accessory_id parameter on saveBoxRecord. Show accessories with visual
indicator (wrench icon + orange background) in boxing detail page.

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

lib/pages/boxing/boxing_api_actions.dart

@@ -65,6 +65,8 @@ class BoxingApiActions {
     required String zongpaiNo,
     required int boxNo,
     required int quantity,
+    String itemType = 'product',
+    int? accessoryId,
   }) async {
     final baseUrl = await _requireBaseUrl();
     if (baseUrl == null) return _missingApiUrl();
@@ -74,6 +76,8 @@ class BoxingApiActions {
       zongpaiNo: zongpaiNo,
       boxNo: boxNo,
       quantity: quantity,
+      itemType: itemType,
+      accessoryId: accessoryId,
     );
     return _saveResult(result, fallbackMessage: '提交失败');
   }