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/parts/boxing_submit_part.dart

@@ -158,4 +158,47 @@ extension _BoxingSubmitPart on _BoxingPageState {
       const Duration(milliseconds: 1500),
     );
   }
+
+  Future<void> _submitAccessory(PendingAccessory accessory) async {
+    if (_zongpaiNo == null || _isSubmitting) return;
+
+    final boxNo = int.tryParse(_boxNoController.text);
+    if (boxNo == null || boxNo <= 0) {
+      this._showStatusOverride(
+        '请先输入有效箱号',
+        StatusDotColor.red,
+        const Duration(seconds: 2),
+      );
+      return;
+    }
+
+    setState(() => _isSubmitting = true);
+
+    final action = await _apiActions.saveBoxRecord(
+      zongpaiNo: _zongpaiNo!,
+      boxNo: boxNo,
+      quantity: accessory.quantity,
+      itemType: 'accessory',
+      accessoryId: accessory.accessoryId,
+    );
+
+    if (!mounted) return;
+
+    setState(() => _isSubmitting = false);
+
+    if (action.success) {
+      _feedbackService.trigger(FeedbackEvent.submitSuccess);
+      // Refresh box info to update pending accessories
+      await this._queryBoxInfo(_zongpaiNo!);
+      if (mounted) {
+        this._showStatusOverride(
+          '${accessory.accessoryType} 已加入箱号 $boxNo',
+          StatusDotColor.green,
+          const Duration(milliseconds: 1500),
+        );
+      }
+    } else {
+      this._showActionError(action, fallback: '附件装箱失败');
+    }
+  }
 }