Heat-map texture set: ramp-coloured color, flat normal, constant mr.
Effective scalar range used for normalisation.
Per-vertex UVs matching the projection used to paint the colour
map. Length is 2 × vertexCount. Values lie in [0, 1],
mapping to the painted texture exactly once across the
geometry's AABB on the picked projection axes. Stored as
Float32Array so it slots straight into
SceneGeometry.uvsCompressed (which the renderer reads as raw
floats and fract()s per-fragment for tiling).
Result of paintHeatMap.