design(prototype): 渲染新 IA 视觉稿(桌面+移动)— 含 bell 图标单源 + 通知/邀请预留

- icons.js 加 bell(codegen→pangolin_icons.dart,L1 同集 59)
- 侧栏提 Account 为一级/顶栏通知铃铛/Account 重排(购买&订单&兑换 + 邀请好友)
- Settings 归三组(连接/外观/关于)+ Web 链接降级;Contact 单源;兑换码仅码
- 通知收件箱 + 邀请好友 占位屏(细节各自 Spec ②③)

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

client/lib/widgets/pangolin_icons.dart

@@ -9,6 +9,7 @@ class PangolinIcons {
   static const link = LucideIcons.link;
   static const ticket = LucideIcons.ticket;
   static const users = LucideIcons.users;
+  static const bell = LucideIcons.bell;
   static const copy = LucideIcons.copy;
   static const refreshCw = LucideIcons.refreshCw;
   static const qrCode = LucideIcons.qrCode;