- Add TrackDownloadLicenseChecker to verify paid track download rights
- Check marketplace license when track is sold as product and user is not owner
- Return 403 with 'purchase required' message when license missing
- Add DATABASE_READ_URL config and InitReadReplica in database package
- Add ForRead() helper for read-only handler routing
- Update TrackService and TrackSearchService to use read replica for reads
- Document setup in DEPLOYMENT_GUIDE.md and .env.template