The lightning system (lightning.hpp/cpp) was fully implemented but never
wired into the renderer. Connect it now:
- Enable lightning during server storm weather (wType==3, intensity>0.1)
and heavy rain (wType==1, intensity>0.7) as a bonus visual
- Scale lightning intensity proportionally to weather intensity
- Render in both parallel (SEC_POST) and fallback rendering paths
- Update and shutdown alongside the weather system
- Show active lightning info in the performance HUD weather section