Join a match by name (or by an existing personal token)

Outcomes: joined, waitlisted, already_in, full, or requested when the player's level is outside the match's range, or declared but unconfirmed on a match that takes confirmed levels only (the organizer approves on the match page; a coach's or the club's confirmation seats the player). A player who already played a finished, scored match with the organizer is never held by that organizer's range. A place the organizer holds for the same name ("Danny") refuses the join with 409 name_held, and nothing is written: if it is that person, they take the place on the match page; if not, they join with a fuller name, such as a last name. A name given without a token that a player in the match (seated or waiting) already carries refuses the join with 409 name_seated, and nothing is written: if it is that player, call again with their personal token; if not, join with a fuller name.