Spread vehicle preparation across frames

I spread vehicle mesh preparation across frames and cached repeated collision decomposition. Vehicle lights use a fixed pool, and scene preparation includes shader warm-up before the vehicle is needed.

A matched isolated spawn check reduced its largest measured stall from 583 to 83 milliseconds. That is a bounded development measurement, not a promise of smooth driving everywhere: the separately reported multi-second native-host freeze remains unresolved. The clips show the current vehicle, not a recreated before-and-after benchmark.

“Vehicle construction and collision preparation share work across frames instead of repeating the same setup.”