Interface KinematicSystemOptions

Execution order key (§39). Default PRIORITY_KINEMATICS — step 4, "kinematic motion". Read once, at registration.

MotionSystem defaults to the same priority; two systems of equal priority run in registration order (§39 registry rule 2). They do not collide in practice — a node driven by a KinematicController is prescribing its pose outright, so giving it a MotionComponent as well means two writers under one authority, which §42 cannot catch. Pick one per node.