feat(client): 三端布局架构 + macOS 桌面端 + app 图标

三端布局(mobile/tablet/desktop):
- core/responsive/form_factor.dart 形态判定 + shell/ 分发器(home_shell→desktop/mobile)
- desktop_shell 对照 ui_kits/desktop/dapp.jsx: 侧栏204·6项 + 套餐卡 + 顶栏(标题/状态/主题切换) + 连接页居中单列
- 新增组件 nav_sidebar / plan_badge_card / content_top_bar / bottom_tab_bar
- 新增一级页 contact_page / settings_page; navigation_provider(NavView)
- 删除旧 widgets/home_shell.dart(逻辑迁入 shell/)

macOS 桌面端:
- 窗口默认 920×600 + 最小 720×560(MainFlutterWindow.swift)
- app 图标替换为穿山甲(AppIcon.appiconset 全套, 由 app-icon.svg 渲染)

其余(本会话):
- Phase2 接线: auth_api/token_store/auth_provider/vpn_bridge_provider + 真实 connection/nodes
- lucide_icons 兼容补丁(packages/lucide_icons_patched) 修复 IconData final 报错
- 测试修复: connect_passthrough(UTF-8) / harness / golden @Skip
- l10n 新增 settingsTitle

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

client/lib/shell/home_shell.dart

@@ -0,0 +1,27 @@
+// home_shell.dart — 主框架分发器（按 formFactor 选三端外壳）
+//
+// desktop → 侧栏 6 项 + 顶栏（对照 ui_kits/desktop）
+// tablet  → 暂用 MobileShell（TODO: TabletShell 侧栏双栏，对照 ui_kits/tablet）
+// mobile  → 底 Tab + 滑动（对照 ui_kits/mobile）
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import '../core/responsive/form_factor.dart';
+import '../pangolin_theme.dart';
+import 'desktop_shell.dart';
+import 'mobile_shell.dart';
+
+class HomeShell extends ConsumerWidget {
+  const HomeShell({super.key});
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    final c = context.pangolin;
+    final Widget body = switch (context.formFactor) {
+      FormFactor.desktop => const DesktopShell(),
+      FormFactor.tablet => const MobileShell(), // TODO: TabletShell
+      FormFactor.mobile => const MobileShell(),
+    };
+    return Scaffold(backgroundColor: c.bg, body: body);
+  }
+}