move_memory MCP tool

AI clients can now move any memory to a different space using the new move_memory tool. The memory's id, full version history, creation date, and all attached assets travel with it automatically. Space editors (not just the memory owner) can move memories between shared spaces; only the owner can pull a memory into their personal vault to prevent silent visibility loss. The tool returns pre-move notices whenever a move reduces access — including a count of members who will lose visibility — so the AI can inform the user before acting.