fyr_ground

Moorland terrain for the pyre part, applied to a Geo.grid mesh spawned by p_fire. The vertex stage displaces by a low-frequency height field (flattened inside the stone circle); the fragment re-derives the analytic normal, blends dirt / moss / bare rock by noise and slope, chars a scorch ring with a pulsing coal bed at the center, and lights with the cool moon key plus a flickering fire point light shadowed analytically by the eight standing stones (menhir0..7 = world x, z, halfWidth, height — set once by the part at build). Per-frame the part drives game_t, flick and ember_glow.