[context menu] The menu doesn't close when the focus leaves the page

# Bug report

## Current behavior

On Youtube, if I open the context menu and then click on another page / software, the menu closes.
With Base UI one, it remains open.

https://github.com/user-attachments/assets/7c3ed520-c0a2-40e9-90d3-a11a04d61015

## Expected behavior

The menu should close when clicking outside of the current page.

## Reproducible example

[Base UI doc](https://base-ui.com/react/components/context-menu)

## Base UI version

1.0.0-beta.4

## Which browser are you using?

Chrome

## Which OS are you using?

Linux Mint 22.2

## Which assistive tech are you using (if applicable)?

None

## Additional context

None