Added lightning scars and thunder variants

I made a ground lightning strike leave a dark scar at its actual impact point. It lasts three minutes and fades near the end, giving the storm a visible aftermath.

Off-screen audio-only events do not invent a mark at the camera. I also integrated three distinct thunder recordings into the native audio library. The clips retain recorded game sound; no subjective listening or soundtrack-quality claim accompanies this update.

“A ground strike leaves a fading scar for three minutes, with three native thunder recordings.”