Stability and API safety improvements
- Added a backend health check before requesting an Openplanet auth token.
- Increased auth retry backoff from 5 seconds to 60 seconds when the backend is unavailable.
- This prevents excessive Openplanet auth traffic if the backend is down.
Hosting and reliability
- Migrated backend hosting to a dedicated Railway deployment for improved stability and uptime.
- Updated deployment setup for Bun + Nixpacks to better support consistent production builds.
Backend migration: MongoDB -> SpacetimeDB
- Replaced MongoDB persistence with a SpacetimeDB-based data layer.