The integration wrapped the final gamma colour in fog_sky_horizon, whose weight
is 1 at 0 deg, so the sunset glow was erased at the horizon. Mix the Modern far
fog colour into the linear gradient before the glow and stars (review A1) and
return from the SKY_FX branch; the Classic tail keeps fog_sky_horizon.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
