inventory_app backend v0.2.0

endpoints:
  GET  /health
  GET  /app/version
  POST /auth/register
  POST /auth/login
  POST /auth/refresh
  POST /sync/push
  GET  /sync/pull?since=N
  POST /files/image
  GET  /files/image/<id>
  GET  /public/store
  GET  /public/products
  POST /public/orders
  GET  /public/orders?order_id=&phone=
  POST /license/activate
  POST /license/verify
  GET  /admin/license（手机发码台，需 X-Admin-Token）