Mythic Masters: beast art still weak (dark creatures, materials, normals) #3096

Split from #3070 (its gallery-signal item shipped). Still open:

• Dark creatures (Black Shuck, Cadejo, Mothman, Hidebehind, Kelpie, Minotaur) read as one value: per-sheet hue shifts or a lighter secondary colour, not a global lift.
• Materials do not separate: horns, claws, eyes, teeth are tiny and nothing reads wet, glossy or metal. Try an env-map specular or matcap term on those materials, and bigger sheet parts.
• No custom or weighted normals: transfer normals from a smooth proxy so low-poly skin shades smooth.
  All in apps/mythic-masters/blender/beast.py and the sheets; judge with bun scripts/beasts.ts --judge.