fix(client): 修复标签打印预览三个问题

- 打印完成后自动关闭预览弹窗
- 打印机列表改为仅显示热敏打印机，无热敏打印机时显示"无打印机可用"并禁用打印按钮
- 库存列表表格行"打标签"按钮改为调用预览弹窗（之前仍走旧直接打印逻辑）

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

client/lib/core/utils/print_util_stub.dart

@@ -501,7 +501,7 @@ Future<List<String>> listLabelPrintersImpl() async {
         return (r.stdout as String)
             .split('\n')
             .map((s) => s.trim())
-            .where((s) => s.isNotEmpty)
+            .where((s) => s.isNotEmpty && _isThermalName(s))
             .toList();
       }
     } catch (e) {
@@ -511,7 +511,10 @@ Future<List<String>> listLabelPrintersImpl() async {
   }
   if (Platform.isWindows) {
     try {
-      return (await Printing.listPrinters()).map((p) => p.name).toList();
+      return (await Printing.listPrinters())
+          .map((p) => p.name)
+          .where((n) => _isThermalName(n))
+          .toList();
     } catch (e) {
       debugPrint('[label] listPrinters 失败: $e');
     }