feat(client): pay v2 支付渠道 switch + 订单列表/详情端到端

购买/支付(Phase B):
- 新 SegSwitch 段控 widget(镜像 .segswitch 原子)
- 购买页重构:顶部支付渠道 switch(默认 USDT→加密货币 / 人民币→支付宝),套餐价随渠道分币种显示,删底部弹窗选方式;点购买直达支付页
- 支付页加订单信息卡(套餐/渠道/金额按币种)
- models:PayChannel + PayCatalogItem.priceUsdtMicro/priceLabel(ch)/perMonthLabel(ch)

订单(P0,全新):
- payment_api.listOrders() + orders_provider(列表 + 详情 family)
- OrdersScreen 列表→详情(状态 pill / 可复制订单号 / 继续支付·重新购买)
- 导航:NavView.orders + desktop_shell 分支 + account 入口

配套:
- l10n +19 getter(支付渠道 4 + 订单 15)×6 语言,l10n 闸绿
- 图标单源迁移 lucide_icons_flutter + pangolin_icons.dart(codegen)
- 联系渠道订正(Telegram/邮件 support@yanmeiai.com/官网) + 前端去广告&时长
- 测试:购买 switch 分币种 + 订单列表/空态/详情 + 假 API listOrders;golden 重录
- flutter analyze 0 error,flutter test 226 全绿

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013nMthbVEmQquxBRKb9Fj8u

client/lib/screens/account_page.dart

@@ -12,6 +12,7 @@ import '../state/navigation_provider.dart';
 import '../widgets/account_screens.dart';
 import '../widgets/app_top_bar.dart';
 import '../widgets/pangolin_icons.dart';
+import 'orders_page.dart';
 import 'payment_page.dart';
 import 'purchase_page.dart';
 
@@ -87,6 +88,8 @@ class AccountPage extends ConsumerWidget {
         _Card(children: [
           _NavRow(icon: PangolinIcons.monitorSmartphone, title: t.myDevices, onTap: () => open(NavView.devices, DevicesScreen(t: t))),
           Divider(height: 1, color: c.border),
+          _NavRow(icon: PangolinIcons.ticket, title: t.ordersTitle, onTap: () => open(NavView.orders, OrdersScreen(t: t))),
+          Divider(height: 1, color: c.border),
           _NavRow(icon: PangolinIcons.settings, title: t.settingsTitle, onTap: () => open(NavView.settings, SettingsScreen(t: t))),
           Divider(height: 1, color: c.border),
           _NavRow(icon: PangolinIcons.shoppingBag, title: t.redeemEntry, onTap: () => open(NavView.redeem, RedeemScreen(t: t))),