Improve chat user action required sound

[meganrogge]

@meganrogge I started getting a sound when the window is not focussed and attention is required. This is great!

However the current sound is not good enough. I do not know how to explain it, but it sounds like it is from the 80s.

Let me reopen this so we work on a more polished sound.

@jo-oikawa

Originally posted by @isidorn in #248200

[isidorn]

Thanks Megan.

cc @kkbrooks

[meganrogge]

Feedback from the team was not to enable it by default except for screen reader users.

[isidorn]

I think that's fair feedback. Esp to start with.
Also we should soon have native OS notifications to show if agent mode needs attention.