[menu] How can the `Popover` be rendered over a disabled `Menu.Item`?

# Get help

## Question
What is a recommended method to handle rendering of the `Popover` over a disabled `Menu.Item`? (including the `Item` sub-types like the [CheckboxItem](https://base-ui.com/react/components/menu#checkbox-item).

## Issue
I need to render a `Menu`, where the first item appears as "disabled" with a `Popover` explaining the reason for it. The popover should appear both on click and hover.

| Menu | Popover |
|--------|--------|
| | |

With the following layout, the popover appears on click, _but not on Spacebar press_:
```tsx
{addToLibraryItem}}
/>
```
IIUC, that happens because when the menu is opened with the keyboard, focus lands on the inner menu item. The latter _isn't the trigger_ for the `Popover`.

## Demo
https://codesandbox.io/p/sandbox/popover-over-disabled-menu-item-r7k9fh

## Relations
I believe that the https://github.com/mui/base-ui/issues/2143 is related. There, @KingSora asked how the initial focus can be placed not on the menu item button, but simply on the 1st element.