Global multiplier on every mouse-wheel zoom step (orbit/ortho dolly and
fly forward/back), on top of the per-scene orbit zoom.speed. A
per-MACHINE preference: effective wheel steps vary enough across mice
and drivers that the user may need to turn this down once (Settings >
Input > Zoom Sensitivity) and keep it across scenes. Read LIVE per wheel
event — mutated by config/user-settings.ts, never by scene settings.
Control system configuration