Use resolveStoredTeam() instead of teams()->first() when picking the
next active team after a team deletion or when an admin switches into
a user's account, so a valid stored preference wins over an arbitrary
first team. DeleteTeam now returns null when the deletion leaves the
owner with multiple teams, deferring to the selection screen instead
of guessing. refreshSession also stops persisting current_team_id
while impersonating, so viewing another user's account no longer
overwrites their real last-active team.
Make clearStoredTeamIfMatches perform an atomic conditional UPDATE
so a concurrent team switch isn't clobbered, and call it for the
deleting owner in DeleteTeam so their stored team id doesn't point
at a deleted team. refreshSession now falls back to
resolveStoredTeam() instead of an arbitrary first team. Add a
return type to SelectTeam::render() and tests covering owner
deletion and concurrent-selection preservation.
Reset the user's persisted current_team_id when they are removed from
a team, when their team is deleted, or when refreshSession finds no
team left, so a dangling reference is never restored on next login.
