Replace bit-packed cell flags in the R channel with a direct material ID float pass-through. Food clearing now writes MAT_AIR instead of clearing a bit.
Reserve bits 3-5 for terrain type (0-7) and bits 6-13 for food quality
(0-255) in the world texture R channel. Adds shared TS constants and
matching GLSL defines. world.frag now preserves upper bits when writing
cell data. Infrastructure only — no behavior changes.
