Function useDocOpenMode

Tracks the current document open mode exposed by AcApDocManager.

This composable is designed for UI state that needs to react as soon as a new document starts opening, rather than waiting until activation finishes. To achieve that it listens to documentToBeOpened and uses the event payload's mode field as the source of truth during the open lifecycle.

Behavior:

• Initializes from the currently active document when the viewer instance is already available
• Retries binding after mount when the viewer has not been created yet
• Keeps the returned ref synchronized with the next requested document mode
• Automatically removes listeners and timers when the component unmounts