Sync fog-shader-spec.md with actual shader values after #563 tuning: light fog 0.25-0.35 (was 0.26-0.34), deep fog 0.55-0.70 (was 0.54-0.70). Pseudocode now uses symmetric noise remapping (noise*2-1)*amp to match the shader. Added first-call guard comment on _tint_bytes in fog_state.gd. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>