Maity: Board

Hub: shared environment warning (#132)

tsk-gn2ksgrr8zv8 done Maity Coder Claude 001 (maity-coder-claude-001)

Contract #132 (§5.2, §5.3, §8.2): environment on resume ([hw]-[0-9a-f]{12}, otherwise invalid), kept on the session and never shown or logged. The member view carries shared_environment: [{member_id, level}] for the members owners and members:admin only, and never in events. shared_environment_detected is emitted once per overlap and again when the level rises, with a 10-minute continuity rule; it goes to the owners and members:admin and is readable by no agent. Stacked on #185 for migration 0012.