Dev/UI command handler that drives a single joint by publishing a
synthetic JointState sensor message on [:sensor, :simulated].
This mirrors BB.LiveView.Components.JointControl.send_simulated_position/3
in bb_liveview — when no real actuator is wired up (as in our dev
robot and the default mix bb.add_robot scaffold), publishing a
fake JointState is the pragmatic way to feed position updates
into the dashboard's joints panel. No need for actuator
declarations or simulation: :kinematic.
Returns the state machine to the robot's initial operational state
so the runtime doesn't park in :executing.
Goal shape: %{joint: atom(), angle: float()}.