feat: initialize Ballet Island 微信小程序 with basic structure and functionality

- Add project configuration for WeChat mini program.
- Create skills lock file for Taroify integration.
- Set up app configuration and styles.
- Implement main app component and index page with welcome message.
- Add health check service to verify backend readiness.
- Configure TypeScript settings and global types.

backend/.env.example

@@ -0,0 +1,13 @@
+# Local development only. Set a strong password for a deployed environment.
+PGHOST=127.0.0.1
+PGPORT=5432
+PGDATABASE=ballet_island
+PGUSER=ballet_island
+PGPASSWORD=change-me-for-local-development
+PGSSLMODE=disable
+
+# Host Go process address; Docker always listens on :8080 inside its container.
+HTTP_ADDR=127.0.0.1:8080
+API_PORT=8080
+API_BIND=127.0.0.1
+