[neeerp]

This continues row 202, the mini-dungeon copies (#683).

• Channel change and Cash Shop: players in a copy can do neither. They get the client's own refusal (BLOCKED_SERVER 1 and 2), as Cosmic blocks both.
• CHANGE_LEADER: handing the party to a member in the copy passes the run to them. A new leader anywhere else ends it, and everyone in the copy goes back to the base map's portal 0, as in Cosmic.
• Tests:
  • net handler tests for both refusals;
  • directory test a_mini_dungeon_follows_a_new_leader_in_it_and_closes_for_one_outside;
  • harness mini_dungeons and party_hunting green.
• Docs: map-travel.md. The time limit still runs per player rather than per copy.