Add VIEW_MODE_SIDE define to common shader defines so shaders can
branch on view mode via preprocessor. In side view, ants init by
scanning downward from the top to find the first non-air cell, then
spawn one pixel above it facing downward. Top view keeps the original
center spawn with random angle.
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.
