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.
Aditya Tripathi
f511921895