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/contact_page.dart

@@ -19,10 +19,9 @@ class ContactPage extends ConsumerWidget {
     final t = ref.watch(appTextProvider);
 
     final channels = <({IconData icon, String name, String sub, bool accent})>[
-      (icon: PangolinIcons.send, name: 'Telegram', sub: '@PangolinVPN_bot', accent: true),
-      (icon: PangolinIcons.messageCircle, name: 'LINE', sub: '@pangolinvpn', accent: false),
-      (icon: PangolinIcons.mail, name: t.contactEmail, sub: 'support@pangolin.vpn', accent: false),
-      (icon: PangolinIcons.shoppingBag, name: t.contactStore, sub: 'shop.pangolin.vpn', accent: false),
+      (icon: PangolinIcons.send, name: 'Telegram', sub: '@pangolin_app', accent: true),
+      (icon: PangolinIcons.mail, name: t.contactEmail, sub: 'support@yanmeiai.com', accent: false),
+      (icon: PangolinIcons.globe, name: t.contactWebsite, sub: 'pangolin.yanmeiai.com', accent: false),
     ];
 
     return SingleChildScrollView(