Option to disable animations (or respect prefers-reduced-motion)

Hi!

Is there an option to turn off animations (like the scrolling motion when changing tabs)? It is pretty slow, and also makes me dizzy on the big screen.

It could be a switch in Settings, or this flag could be used to detect this preference automatically:

> The [prefers-reduced-motion](https://developer.mozilla.org/en-US/docs/Web/CSS/@media/prefers-reduced-motion) CSS media feature is used to detect if the user has requested that the system minimize the amount of non-essential motion it uses.

Start by tracing the tab-change scrolling animation and the existing Settings or preferences entry point; the issue names no files. Check how DevTools can detect prefers-reduced-motion, then verify that non-essential animations are disabled or an explicit setting works without changing tab behavior.

索引モデルが issue の本文から書いたものです。