Perbarindo Push Service

Backend for the Perbarindo BPR mobile app's push notifications. It has no user-facing UI — see docs/API_NOTES.md in the repo root for how it works and how to operate it.

• POST /api/register-device — called by the mobile app on login/foreground.
• GET /api/poll — called on a schedule by an external cron to check for new notifications and push them.