Function lut_texture 

pub fn lut_texture(device: &Device, label: &str) -> Texture

Create the shared 256×1 LUT texture a shader-colored scene binds and uploads its baked palette into. Centralized here so the fragment, reaction-diffusion, and attractor scenes stay byte-for-byte consistent (ADR-0021: one source both the GPU and CPU sample). Seed it with write_lut before first use.