Mythic Masters: more beasts, and better ones, through the sheet loop #2733

Part of #2706. PR #2729 added the loop (apps/wildclash/beasts/*.json -> bun run beasts -> Blender build, contact sheet, auto-rig skeleton, IK puppet in the arena) and four beasts: Hodag, Jersey Devil, Jackalope, Agropelter.

Next through that loop:

• One sheet per creature once the folklore roster replaces the API roster (Mythic Masters: creatures from world folklore instead of the API roster, and procedural models #2706 step 2); today BEASTS in src/beasts.ts maps an archetype to a sheet.
• Looks: the skin modifier gives short fat bodies a boxy torso (the jackalope); try more spine nodes, higher subdivision, or a metaball body for the round ones. Wing membranes are flat n-gons; a few extra trailing-edge points scallop them. Materials are flat colours; a belly/back two-tone from the vertex normal would help.
• Motion: heads and tails are unpinned tips that only follow their bones; a look-at goal for the head and a lag on the tail would sell the walk. Attacks don't pose the body yet (a lunge on heavy, a rear on launcher).
• Keep the rule the script enforces: every sheet's feet come out as rig tips, or the row fails.