Sample data and atmospheric glow

Most of today went into getting the offline fallbacks sorted. I added sample datasets for air quality, aurora, ISS, quakes, cities, and submarine cables so the globe never loads blank, even if every API is down. The bigger job was replacing the atmosphere with a proper dual‑shell Fresnel shader. I wanted a subtle rim glow and a bit of surface haze, so I wrote two custom shaders: a back‑side halo and a front‑side haze.