Add Weather::Type::STORM enum value and wire it from SMSG_WEATHER type 3.
Storm particles are faster (70 units/s vs rain's 50), wind-angled at 15+
units lateral velocity with gusty turbulence, darker blue-grey tint, and
shorter lifetime. Previously storms rendered identically to rain.
- Skybox now uses DBC sky colors (skyTop/skyMiddle/skyBand1/skyBand2) instead
of hardcoded C++ color curves, with 3-band gradient and Rayleigh/Mie scattering
- Clouds receive sun direction for lit edges, self-shadowing, and silver lining
- Fixed sun quad box artifact with proper edge fade in celestial shader
- Lens flare attenuated by fog, cloud density, and weather intensity
- Replaced garish green/purple lens flare ghosts with warm natural palette
- Added zone-based weather system for single-player mode with per-zone rain/snow
configuration, probability-based activation, and smooth intensity transitions
- Server SMSG_WEATHER remains authoritative when connected to a server
