Invite a team to a tournament

Invites a team to the tournament and notifies its captains. Requires the tournaments invites capability and ADMIN authority - strictly higher than the MANAGER floor for reading the invite list, because in an INVITE_ONLY tournament the invite is the entry gate; a tournament MODERATOR answers 403. Re-inviting a team reuses that team's existing invite row rather than creating a second one, so retries cannot mint duplicates. Answers 400 error_invalid_input when the team does not exist, plays a different game to the tournament, or already holds a PENDING or ACCEPTED invite.