[popover] Focus is not set to the interactive element when it is in another component

# Bug report

## Current behavior

When Popover's content is changing, focus moves automatically, but is not set to the new interactive element if it is added as a separate component. And works well if the new content is added as a tsx.

Video📽️

https://github.com/user-attachments/assets/63decc30-ab46-453d-9dd8-a286a5025ffa

Looks like this is because of `restoreFocus="popup"` setting in [popover/popup/PopoverPopup.tsx](https://github.com/mui/base-ui/blob/master/packages/react/src/popover/popup/PopoverPopup.tsx#L184).
When I set this property for the ``, it keeps focus on the new element at the same place.
I understand, that this is not good.
It wood be great to be able to reset focus to the first interactive element

## Expected behavior

When the new content is added as a separate component, focus shoud be added to the first interactive element?

## Reproducible example

[CodeSandbox](https://codesandbox.io/p/devbox/competent-phoebe-nm3t7r?workspaceId=ws_Ddd5rrbjzugd76Ymez2gb7)

## Base UI version

1.0.0-beta.4

## Which browser are you using?

Chrome

## Which OS are you using?

Windows