Added documentation for:
- parent_user_id column in User table (hierarchical user management)
- mqtt_credentials table with device authentication
- mqtt_acl_rules table for topic permissions
- mqtt_sync_status table for broker synchronization
- All new database indexes
- Updated ER diagram with new relationships
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
