Plush pigeon physics demo in a WebGPU browser engine

GOAL: Make "Plush Pigeon" (Material Studies No. MOTION: 031) on the Plush Penguin WebGPU engine: XPBD soft-body lattice, shell fur, cloth wings, posture-driven gait, tools Hand / Finger / Comb. The toy: a round, well-fed rock dove of soft grey minky. - Shape: one SDF with a round body, a proud chest, a neck rising into a teal domed head, a flat tail with a dark band, and two pink felt feet with three toes forward and one behind. - Neck ring: iridescent, green above and violet below, dipping lower over the chest. - Face: glossy bead eyes with an orange ring; a small dark felt beak with a pale cere. - Wings: two stuffed cloth wings sewn at the shoulders, folded down and back along the sides, each with two charcoal bars and a darker tip. - Fur length: shorter on the head and neck ring, cropped to felt on the feet. Life: - Strut: a waddle in which neck-cell shear muscles bob the head with every step. Keep the bend normal orthogonal to the neck axis, or the shear pushes the whole body. - Coo: the chest cells swell, the head bows twice, and a synthesized three-note rolling "croo" plays. - Flap: wing flaps with hops and a feather-flutter sound. - Topple, then get back up. - Finger: struts over to a held finger; a boop on the beak makes it coo; it sometimes coos when idle. Palettes: Blue bar, Ash red, Snow. Readouts: mass, volume, steps, coos. Responsive layout.