feat(app): initialize uni-app with routing, stores, and infrastructure

- Vue 3 + TypeScript + Pinia + SCSS
- 3-tab navigation (home, booking, profile) + 11 sub-pages
- HTTP client with JWT auth, request interceptors
- Pinia stores: user (auth, profile, memberships), studio, booking
- Utility functions: price formatting, date helpers
- WeChat login helper
- All pages as stubs ready for implementation

packages/app/src/uni.scss

@@ -0,0 +1,21 @@
+/* uni.scss - 全局样式变量 */
+$brand-color: #1a1a2e;
+$brand-light: #e2d1c3;
+$accent-color: #c9a87c;
+$text-primary: #333333;
+$text-secondary: #666666;
+$text-hint: #999999;
+$bg-page: #f5f5f5;
+$bg-card: #ffffff;
+$border-color: #eeeeee;
+$success-color: #52c41a;
+$warning-color: #faad14;
+$error-color: #ff4d4f;
+$radius-sm: 8rpx;
+$radius-md: 16rpx;
+$radius-lg: 24rpx;
+$spacing-xs: 8rpx;
+$spacing-sm: 16rpx;
+$spacing-md: 24rpx;
+$spacing-lg: 32rpx;
+$spacing-xl: 48rpx;