feat: 错误自动上报机制

- 后端：error_reports 表 + POST /api/v1/public/errors + GET /api/v1/admin/errors
- Flutter：ErrorReporter 单例，60s 去重，fire-and-forget，不影响用户
- main.dart：FlutterError 和 Zone 错误自动上报
- 打印异常：catch 块加 reportError，Windows 打印问题可自动采集堆栈

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

client/lib/core/utils/print_util_stub.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/services.dart';
+import '../errors/error_reporter.dart';
 import 'package:pdf/pdf.dart';
 import 'package:pdf/widgets.dart' as pw;
 import 'package:printing/printing.dart';
@@ -191,7 +192,8 @@ Future<void> printProductLabelImpl({
 
   try {
     await Printing.layoutPdf(onLayout: (_) async => doc.save());
-  } catch (e) {
+  } catch (e, st) {
+    reportError(e, st);
     throw Exception('打印失败，请检查打印机连接和驱动是否正常。\n详情：$e');
   }
 }
@@ -430,7 +432,8 @@ Future<void> printStockInOrderImpl(StockInOrder order) async {
   ));
   try {
     await Printing.layoutPdf(onLayout: (_) async => doc.save());
-  } catch (e) {
+  } catch (e, st) {
+    reportError(e, st);
     throw Exception('打印失败，请检查打印机连接和驱动是否正常。\n详情：$e');
   }
 }
@@ -484,7 +487,8 @@ Future<void> printStockOutOrderImpl(StockOutOrder order) async {
   ));
   try {
     await Printing.layoutPdf(onLayout: (_) async => doc.save());
-  } catch (e) {
+  } catch (e, st) {
+    reportError(e, st);
     throw Exception('打印失败，请检查打印机连接和驱动是否正常。\n详情：$e');
   }
 }