feat(client): P6 DevicesScreen 重做 + DevicePlatform 枚举

回应「状态码用枚举更好」:新增 DevicePlatform 枚举(线格式 fromWire 解析,
UI 只碰枚举,穷尽 switch),Device.platformKind getter;platform 图标按枚举 switch。
DevicesScreen 按 §7 视觉稿重做:行内 名称+「本机」标 / 平台·客户端版本·最后登录 /
在线绿点光晕·离线灰点 + 行尾 ⋯ 菜单(强制退出 / 清除登录信息·危险红)+ 危险二次
确认弹窗;本机行不显示 ⋯(不自我踢)。l10n 新增在线/离线/最后登录/从未登录/强制
退出/清除登录信息/取消 + 确认文案(中英);「当前设备」改「本机」。
新图标 moreVertical/trash/alertTriangle。localDeviceIdProvider 供本机判定。
测试:devices_screen widget 3 例(本机标+在线/离线+版本渲染 / ⋯菜单→强制退出→
确认→POST logout / 清除→DELETE);全量 flutter test 58 绿。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/lib/l10n/strings_en.dart

@@ -128,6 +128,24 @@ class StringsEn extends AppText {
   @override
   String get remove => 'Remove';
   @override
+  String get devOnline => 'Online';
+  @override
+  String get devOffline => 'Offline';
+  @override
+  String get devLastLogin => 'Last login';
+  @override
+  String get devNeverLogin => 'Never logged in';
+  @override
+  String get devForceLogout => 'Force logout';
+  @override
+  String get devClearLogin => 'Clear login info';
+  @override
+  String get devForceLogoutConfirm => 'This revokes the device\'s login session — it will be kicked offline and must sign in again. The device stays in the list.';
+  @override
+  String get devClearLoginConfirm => 'This removes the device from the list entirely and revokes its login session and data-plane credential. The device must sign in again to be used.';
+  @override
+  String get devCancel => 'Cancel';
+  @override
   String get redeemEntry => 'Redeem & buy';
   @override
   String get contactEntry => 'Contact us';