start_jog restored READY for any zero velocity, without checking whether a
motion owned the arm. A teleop source streaming zero-velocity ticks during a
move published moving -> ready mid-motion, and the closing guard in _run_motion
then saw READY rather than MOVING and never republished, so a caller watching
robot_state concluded the motion had finished early.
Route every "the arm has stopped" transition through _idle_unless_busy, which
reports READY only when no motion is running, no jog is driving the arm, and the
state has not already left MOVING for unavailable or recovering.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>