- Extract ownerMap building into app/lib/owner-map.ts to eliminate
duplication across the two loaders
- Guard against null username AND displayName so the map only contains
real string values
- Apply username display to TeamsDraftedGrid (the "Teams" tab in the
active draft room), which was missed in the initial change
https://claude.ai/code/session_01C97GauJaAB83NVWxdpNVh1
