feat(client): 标签打印预览弹窗（打印机选择 + 份数 + 所见即所得预览）

- 新增 LabelData 模型统一聚合单张标签字段（qrBytes/copies 等）
- 抽取 _renderLabelBitmap 共享位图绘制逻辑，TSPL 裸发与预览渲染完全一致
- 新增 renderLabelPreview / listLabelPrinters / detectDefaultPrinter 公开 API
- printProductLabel 新增 printerName 参数，透传到热敏裸发路径
- 新建 LabelPreviewDialog：缩略图条+大图主视图，打印机下拉+记忆（SharedPrefs）
  份数调整、勾选跳过、逐张打印进度状态显示
- 库存/商品详情/入库单 打标签 均接入预览弹窗，移除旧 _LabelPrintDialog

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

client/lib/screens/inventory/inventory_list_screen.dart

@@ -16,6 +16,8 @@ import '../../widgets/multi_select_dropdown.dart' show FilterableColumnHeader;
 import '../../widgets/page_scaffold.dart';
 import '../../core/utils/export_util.dart';
 import '../../core/utils/print_util.dart';
+import '../../core/utils/dialog_util.dart';
+import '../../widgets/label_preview_dialog.dart';
 import '../../providers/product_provider.dart';
 import '../../providers/product_option_provider.dart';
 import '../../providers/tab_state_provider.dart';
@@ -200,21 +202,23 @@ class _InventoryListScreenState extends ConsumerState<InventoryListScreen> {
         await ref.read(productRepositoryProvider).getQRCodeBytes(item.productId!);
     final shopInfo = ref.read(shopInfoProvider).valueOrNull;
     if (!context.mounted) return;
-    await safePrint(
-      context,
-      () => printProductLabel(
-        qrBytes: qrBytes,
-        name: item.productName,
-        code: item.productCode,
-        series: item.series.isEmpty ? null : item.series,
-        spec: item.spec.isEmpty ? null : item.spec,
-        batchNo: item.batchNo.isEmpty ? null : item.batchNo,
-        productionDate: item.productionDate,
-        remark: item.remark.isEmpty ? null : item.remark,
-        shopName: shopInfo?.name ?? '',
-        shopAddress: shopInfo?.address ?? '',
-        shopPhone: shopInfo?.phone ?? '',
-      ),
+    final label = LabelData(
+      productId: item.productId,
+      qrBytes: qrBytes,
+      name: item.productName,
+      code: item.productCode,
+      series: item.series.isEmpty ? null : item.series,
+      spec: item.spec.isEmpty ? null : item.spec,
+      batchNo: item.batchNo.isEmpty ? null : item.batchNo,
+      productionDate: item.productionDate,
+      remark: item.remark.isEmpty ? null : item.remark,
+      shopName: shopInfo?.name ?? '',
+      shopAddress: shopInfo?.address ?? '',
+      shopPhone: shopInfo?.phone ?? '',
+    );
+    showAppDialog(
+      context: context,
+      builder: (_) => LabelPreviewDialog(labels: [label]),
     );
   }