social.colibri.beta.thread.moveMessages

Moves messages into another thread or channel. A message lives in its author's own repo and cannot be rewritten by a moderator, so the move is a `moved` label written into the source space for each message. The destination serves each moved message at its own record key, so a selection keeps the order it was written in and reads among the destination's own messages by send time. The AppView withholds a moved message from the space it came from.