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/android/app/build.gradle

@@ -0,0 +1,67 @@
+def localProperties = new Properties()
+def localPropertiesFile = rootProject.file('local.properties')
+if (localPropertiesFile.exists()) {
+    localPropertiesFile.withReader('UTF-8') { reader ->
+        localProperties.load(reader)
+    }
+}
+
+def flutterRoot = localProperties.getProperty('flutter.sdk')
+if (flutterRoot == null) {
+    throw new GradleException("Flutter SDK not found. Define location with flutter.sdk in the local.properties file.")
+}
+
+def flutterVersionCode = localProperties.getProperty('flutter.versionCode')
+if (flutterVersionCode == null) {
+    flutterVersionCode = '1'
+}
+
+def flutterVersionName = localProperties.getProperty('flutter.versionName')
+if (flutterVersionName == null) {
+    flutterVersionName = '1.0'
+}
+
+apply plugin: 'com.android.application'
+apply plugin: 'kotlin-android'
+apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
+
+android {
+    namespace "com.pangolin.pangolin_vpn"
+    compileSdkVersion flutter.compileSdkVersion
+    ndkVersion flutter.ndkVersion
+
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
+
+    kotlinOptions {
+        jvmTarget = '1.8'
+    }
+
+    sourceSets {
+        main.java.srcDirs += 'src/main/kotlin'
+    }
+
+    defaultConfig {
+        applicationId "com.pangolin.pangolin_vpn"
+        minSdkVersion flutter.minSdkVersion
+        targetSdkVersion flutter.targetSdkVersion
+        versionCode flutterVersionCode.toInteger()
+        versionName flutterVersionName
+    }
+
+    buildTypes {
+        release {
+            signingConfig signingConfigs.debug
+        }
+    }
+}
+
+flutter {
+    source '../..'
+}
+
+dependencies {
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
+}