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/macos/Flutter/GeneratedPluginRegistrant.swift

@@ -7,12 +7,14 @@ import Foundation
 
 import file_picker
 import package_info_plus
+import printing
 import shared_preferences_foundation
 import url_launcher_macos
 
 func RegisterGeneratedPlugins(registry: FlutterPluginRegistry) {
   FilePickerPlugin.register(with: registry.registrar(forPlugin: "FilePickerPlugin"))
   FPPPackageInfoPlusPlugin.register(with: registry.registrar(forPlugin: "FPPPackageInfoPlusPlugin"))
+  PrintingPlugin.register(with: registry.registrar(forPlugin: "PrintingPlugin"))
   SharedPreferencesPlugin.register(with: registry.registrar(forPlugin: "SharedPreferencesPlugin"))
   UrlLauncherPlugin.register(with: registry.registrar(forPlugin: "UrlLauncherPlugin"))
 }