nx_creature_motion.nx

nx_creature_motion.nx -- UNIFY swap + motion: pose the smin SDF body from the FK rig (nx_bodypose) AND add nx_assetvariant SWAP SLOTS (horns/ears/tail/build) as parts BONE-ANCHORED to the head/pelvis, so the swapped features ANIMATE WITH the creature (a horned head turns and the horns swing; a tail rides the hips). This is the operator's convergence: one asset reused (a synthetic body), diversified by swapping, and given motion -> video. Fills the nx_sdfrender base each frame; renders on the production skin shader. license_tier: ORIGINAL