Add winner avatar display and opponent invite feature
Winner Display:
- Add winner field to database schema
- Display winner's avatar in archive cards instead of "completed" badge
- Emphasize winner's name in player list with bold styling
- Fetch user profiles for avatars
- Show trophy emoji placeholder if no avatar available
Opponent Invite:
- Add opponent handle input field to create game form
- Resolve Bluesky handle to DID on server-side
- Create game directly with opponent (status=active) instead of waiting room
- Add validation (handle not found, can't play self)
- Update button text based on whether opponent is specified
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>