_add_team_members_to_team reconciled membership by reading the complete_team_data
snapshot captured at the start of team_member_add, appending in memory, and
writing the whole members_with_roles array back. Two concurrent /team/member_add
calls for the same team read the same snapshot, so the last write wins and one
member is silently lost. This affects every concurrent team member add, including
the SCIM group PATCH op:add path that routes through team_member_add
Reconcile members_with_roles inside a transaction that locks the team row with
SELECT ... FOR UPDATE before re-reading the current membership, so concurrent
writers serialize on the row lock and each appends onto the other's committed
result. The interactive transaction is exposed through a thin PrismaClient.tx()
passthrough and the locked read is encapsulated in
TeamRepository.get_members_with_roles_locked, and the SCIM group PATCH applies
membership as deltas so concurrent adds are not clobbered
