Hover text for Regenerate button

[novoselt]

The models in the @ mentions list should have some short explanations, I think the same as for the AI button at the top.

The Regenerate button itself should have a tip like "Not happy with the answer? Regenerate it using the same model or pick a more advanced one from the dropdown!"

The goals are 1) point out that there is the dropdown and 2) encourage experimentation with other models, specifically "more advanced ones" ;-)