Mythic Masters: signature motions per creature (grabs, head shakes, belly drum, tail volley, shriek) #2809

Part of #2802 (the moves front, round 2), after PR #2810. One worker, from main. Owns apps/wildclash/src/beasts.ts (the Puppet), src/creatures.ts (a motion on each sig) and test/beasts.test.ts. The effects-side round 2 is #2820, in other files.

Every ultimate uses the shared coil-and-snap of its fx today. Give the signatures a motion of their own, driven by attackPose's wind and k so the anticipation stays:

• grab (the drain signatures: kelpie, ahuizotl, chupacabra, lambton-worm, ushi-oni): the head and front feet reach for the target through the wind-up and pull back on the strike.
• shake (the multi-headed: hydra, chimera, zmey): the head tips swing out of phase.
• drum (tanuki): the body bounces and the front feet beat the belly.
• volley (manticore): the tail rears over the back and flicks.
• shriek (jersey-devil, ozark-howler, mothman): the head thrown back and the body up on the hind legs, wings wide.
• roll (tarasque, hodag): the body dips and the back arches as it charges.

A motion field on sig in creatures.ts (default: none), read in Puppet.update. A test per motion that compares a head or foot against the same beast standing, like the heavy and launcher tests there. Judge in a fight per creature side-on (window.wildclash.camera("side"); freeze a frame with a requestAnimationFrame wrapper as PR #2810 did). Before and after screenshots, scored out of 10, in the PR. No sheet, stat or fx changes.