Drag/drop stops working when the calendar is rendered into another document (portal to a separate window or iframe)

Check that this is really a bug

• I confirm

Reproduction link

https://codesandbox.io/p/sandbox/d5hvhs

Bug description

Selection attaches its mouse/drag listeners and runs document.elementFromPoint hit-testing and pageOffset scroll math against the module-global document/window. When a calendar is rendered into a different document (e.g. a React portal into a window.open window, or an iframe), those listeners are bound to the host page's document and never receive the events fired in the calendar's own window. Result: event move/resize and drag-from-outside silently do nothing. Ordinary clicks and other React-handled interactions still work (React delegates synthetic events to the portal correctly), only RBC's own native listeners are mis-targeted.

To Reproduce

1. Render withDragAndDrop(Calendar) into a portal whose container lives in a separate window.open document.
2. Try to move/resize an event, or drag an external item onto the calendar.
3. Nothing happens (the same calendar works in-page).

Expected Behavior

Drag/resize/drop work regardless of which document the calendar is rendered into.

Actual Behavior

Drag/resize/drop do not work in the other document.

react-big-calendar version

1.20.0

React version

19.2.4

Platform/Target and Browser Versions

macOS Chrome 149.0.7827.199

Validations

• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.
• Make sure this is a react-big-calendar issue and not an implementation issue

Would you like to open a PR for this bug?

• I'm willing to open a PR