fix: 修复打印中文乱码、XLS导入100条截断、Nginx图片路由

- 打印改为 Web 平台用 HTML+CSS 方案，避免 pdf 包中文字体 bug
- 新增 print_util.dart 条件导入层（web/stub），彻底隔离 platform channel
- XLS 导入不再依赖 DIMENSIONS 记录的 MaxRow，改为读到连续5空行停止
- Nginx /images/ 加 ^~ 前缀，防止 .jpg 正则 location 拦截

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

client/lib/screens/products/product_detail_screen.dart

@@ -4,10 +4,8 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
-import 'package:pdf/pdf.dart';
-import 'package:pdf/widgets.dart' as pw;
-import 'package:printing/printing.dart';
 import '../../core/config/app_config.dart';
+import '../../core/utils/print_util.dart';
 import '../../core/theme/app_theme.dart';
 import '../../models/product.dart';
 import '../../models/product_image.dart';
@@ -527,36 +525,15 @@ class _QRCodeDialogState extends ConsumerState<_QRCodeDialog> {
 
   Future<void> _print() async {
     if (_bytes == null || _printing) return;
-    setState(() { _printing = true; _printStatus = '正在准备字体...'; });
+    setState(() { _printing = true; _printStatus = '正在打印...'; });
     try {
-      final fontData = await rootBundle.load('assets/fonts/NotoSansSC-Regular.ttf');
-      if (mounted) setState(() => _printStatus = '正在生成 PDF...');
-      final font = pw.Font.ttf(fontData);
       final p = widget.product;
-      final doc = pw.Document();
-      final qrImage = pw.MemoryImage(_bytes!);
-      doc.addPage(pw.Page(
-        pageFormat: PdfPageFormat.a4,
-        build: (_) => pw.Center(
-          child: pw.Column(
-            mainAxisSize: pw.MainAxisSize.min,
-            children: [
-              pw.Image(qrImage, width: 200, height: 200),
-              pw.SizedBox(height: 12),
-              pw.Text(p.name,
-                  style: pw.TextStyle(font: font, fontSize: 18, fontWeight: pw.FontWeight.bold)),
-              pw.SizedBox(height: 4),
-              pw.Text('编号：${p.code}',
-                  style: pw.TextStyle(font: font, fontSize: 13)),
-              if ((p.spec ?? '').isNotEmpty)
-                pw.Text('规格：${p.spec}',
-                    style: pw.TextStyle(font: font, fontSize: 13)),
-            ],
-          ),
-        ),
-      ));
-      if (mounted) setState(() => _printStatus = '正在打开打印...');
-      await Printing.layoutPdf(onLayout: (_) async => doc.save());
+      await printProductLabel(
+        qrBytes: _bytes!,
+        name: p.name,
+        code: p.code,
+        spec: p.spec,
+      );
     } catch (e) {
       if (mounted) {
         ScaffoldMessenger.of(context).showSnackBar(