Generate text-driven skeletal animations for an already-rigged 3D model. Pass the rigged GLB in `model` (URL or base64) and a motion `prompt` (e.g. "walking", "swinging its axe"). The model must already have a skeleton — rig it first via the rig endpoint if not. Synchronous: returns num_variants candidate animations (default 4), each a standalone animation-only GLB (skeleton + one clip, no mesh) in `glb_url` plus an mp4 `preview_url`, so you can pick the best one and fuse it with your model in a game engine or three.js. mode selects the representation — rot_trans (default, most faithful) or rot_only (for retargeting). Animation quality is hit-or-miss, which is why multiple candidates are returned. Credits are charged once per call regardless of variant count, only on success. Requires an API key (user scope).