feat(tsk_iRa5iBC4v7Tu): Flutter 客户端工程搭建(演示态)

基于 design/flutter/ 起步包在 client/ 下建立 Flutter 工程：

- pubspec.yaml：flutter_svg / lucide_icons / google_fonts 依赖；
  SVG 资产注册；字体由 google_fonts 运行时加载，无需本地 ttf
- lib/pangolin_theme.dart：完整设计令牌（色阶 / 间距 / 圆角 /
  动效 / 文字阶），PangolinText 改用 GoogleFonts getter，
  PangolinTheme.light / .dark 开箱即用
- lib/main.dart：runApp + 明暗主题 + 登录 → 引导 → 主框架 RootFlow
- lib/widgets/：全套组件雏形
    pangolin_icons    Lucide 图标映射
    pangolin_button   胶囊按钮四态
    country_code      国家码块 + 信号条
    status_pill       色点胶囊
    connect_button    核心连接键三态（off/connecting/on + 动画）
    server_tile       服务器列表行
    plan_card         套餐卡（专业版渐变高亮）
    auth_screen       登录 / 注册（邮箱验证码 + 设密码）
    onboarding_screen 首次引导 PageView（3 屏可滑动 + 进度点）
    home_shell        底部 4 Tab（连接/节点/统计/账户 + 状态机）
    account_screens   套餐选择 / 设备管理 / 兑换 / 联系我们
    pangolin_logo     PangolinMark / BrandLockup / AppIcon（SVG）
- assets/：logo-mark / logo-mark-white / logo-wordmark / app-icon（SVG）
- android/：Kotlin 主 Activity + Manifest + Gradle 配置
- ios/：Runner.xcodeproj + xcscheme + Podfile + AppDelegate + storyboard

运行方式（cd client/）：
  flutter pub get && flutter run

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

client/lib/widgets/pangolin_button.dart

@@ -0,0 +1,66 @@
+// pangolin_button.dart — 胶囊按钮(primary / secondary / ghost / danger)
+import 'package:flutter/material.dart';
+import '../pangolin_theme.dart';
+
+enum PangolinButtonVariant { primary, secondary, ghost, danger }
+
+class PangolinButton extends StatelessWidget {
+  const PangolinButton({
+    super.key,
+    required this.label,
+    this.onPressed,
+    this.icon,
+    this.variant = PangolinButtonVariant.primary,
+    this.expand = false,
+  });
+
+  final String label;
+  final VoidCallback? onPressed;
+  final IconData? icon;
+  final PangolinButtonVariant variant;
+  final bool expand;
+
+  @override
+  Widget build(BuildContext context) {
+    final c = context.pangolin;
+    final disabled = onPressed == null;
+
+    late final Color bg, fg;
+    Border? border;
+    switch (variant) {
+      case PangolinButtonVariant.primary:
+        bg = c.accent; fg = c.fgOnAccent; break;
+      case PangolinButtonVariant.secondary:
+        bg = c.surface; fg = c.fg1; border = Border.all(color: c.borderStrong, width: 1.5); break;
+      case PangolinButtonVariant.ghost:
+        bg = Colors.transparent; fg = c.accent; break;
+      case PangolinButtonVariant.danger:
+        bg = c.dangerSubtle; fg = c.danger; break;
+    }
+
+    final child = Row(
+      mainAxisSize: expand ? MainAxisSize.max : MainAxisSize.min,
+      mainAxisAlignment: MainAxisAlignment.center,
+      children: [
+        if (icon != null) ...[Icon(icon, size: 18, color: fg), const SizedBox(width: 8)],
+        Text(label, style: PangolinText.sm.copyWith(color: fg, fontWeight: FontWeight.w600, fontSize: 15)),
+      ],
+    );
+
+    return Opacity(
+      opacity: disabled ? 0.45 : 1,
+      child: Material(
+        color: bg,
+        shape: StadiumBorder(side: border?.top ?? BorderSide.none),
+        clipBehavior: Clip.antiAlias,
+        child: InkWell(
+          onTap: onPressed,
+          child: Padding(
+            padding: const EdgeInsets.symmetric(horizontal: 22, vertical: 13),
+            child: child,
+          ),
+        ),
+      ),
+    );
+  }
+}