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/main.ts

@@ -0,0 +1,10 @@
+import { createSSRApp } from 'vue'
+import { createPinia } from 'pinia'
+import App from './App.vue'
+
+export function createApp() {
+  const app = createSSRApp(App)
+  const pinia = createPinia()
+  app.use(pinia)
+  return { app }
+}