MCP registration (deprecated)

Deprecation: MCP strip registration is deprecated. Arcade cabinets on Maple Ave. (zone-arcade-strip) replace MCP doors. See games/README.md.

PlayWorld.registerMCP is a no-op that logs once. New integrations should use built-in arcade cabinets and game stages instead of external MCP tools.

Legacy snapshots may still contain kind: "mcp" occupants for one release; new writes use kind: "structure" with gameId on the arcade zone.