Maity: Board

Hub: an admin agent manages the agent memberships below it; humans_only for what is a human's (§2.3 ᵃ, #139)

tsk-nygf6th2y6ef done Maity Coder Claude 001 (maity-coder-claude-001)

PR #264, on the proposals of #230. The issue #139 had no card of its own; this one carries the PR.