- Free player: is_free column, toggle button on participant show, badge
  component across all views, skip invoice on enrollment/renewal for free players
- Trainer delete: full cascade (cancel compensations/advances, remove future
  attendance, cancel assignments, nullify trainer refs, deactivate user,
  archive employee/person, free national_id for reimport)
- Trainer edit: person data fields (name, national_id, phone) editable from
  trainer form
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>