Replace single `_checked_team: Optional[Team]` with `_checked_teams: dict[int, Team]`
keyed by `interaction.user.id`. The previous single field was shared across all
concurrent interaction tasks, allowing User B's interaction_check to overwrite
`_checked_team` before User A's button handler read it — crediting the wrong team.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>