Adds a `not_participating` boolean column to `event_results` so admins can
mark a participant as not competing in a specific upcoming major (e.g. Alcaraz
withdrawing from Wimbledon due to injury). The golf, tennis, and CS2 major
simulators now query this flag for incomplete events and exclude those
participants from the event's draw/field, redistributing probability weight
to the remaining field. Admin UI for qualifying major_tournament events gains
a "Not Participating" card to mark/unmark withdrawals before the event runs.
https://claude.ai/code/session_01HxNPLEXzr5Km3suWrJe2F9
