feat(client): settings 完整版(开关组) + 联系/设置整页 golden

- settings_page 补全对照 dapp.jsx DSettings: 功能开关组(开机自启/智能分流/
  Kill Switch, 本地演示态) + 配置组补检查更新行; 改 ConsumerStatefulWidget 持开关态
- l10n 新增 autostart/smartRoute/killSwitch(+Sub) + checkUpdate(中英)
- desktop 整页 golden 补 联系页 + 设置页(凑齐可截 5 页: 节点/统计/账户/联系/设置)

测试: flutter test 81 通过(+2 golden), analyze 0 error

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

client/lib/l10n/strings_en.dart

@@ -125,6 +125,20 @@ class StringsEn extends AppText {
   String get protocol => 'Protocol';
   @override
   String get settingsTitle => 'Settings';
+  @override
+  String get autostart => 'Launch at startup';
+  @override
+  String get autostartSub => 'Run automatically on system start';
+  @override
+  String get smartRoute => 'Smart routing';
+  @override
+  String get smartRouteSub => 'Accelerate abroad, direct at home';
+  @override
+  String get killSwitch => 'Kill Switch';
+  @override
+  String get killSwitchSub => 'Block traffic if the link drops';
+  @override
+  String get checkUpdate => 'Check for updates';
 
   @override
   String get choosePlan => 'Choose plan';