MCP: set the rack position when moving a thing into a rack #547

What you're trying to do

Put things into a rack through MCP, e.g. move two switches into the rack that already holds the router.

What gets in the way today

move_thing takes to_place_id / to_container_id only. The thing lands in the rack without a position, so it does not show in the rack view until someone sets U and face in the app. get_thing already returns rack: { units, u, face, full }, so the data is there — it just can't be written.

What you'd like

Optional rack fields on move_thing (and update_thing for an item already in the rack): u, face, units, full. Moving into a rack without them keeps today's behaviour; giving a U that is taken returns a validation error that names the occupying thing.