Enhance setup wizard: grid builder, groups, participants import

Setup wizard now covers 10 steps (was 8):
- Facilities step includes visual grid layout builder (rows×columns)
- New Groups step: create groups with interactive segment multi-select
- New Participants step: import existing players with guardian data
- completeSetup() creates SpaceLayout + SpaceSegments for each facility grid
- Hint encourages max division for scheduling flexibility
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>