How do I move a room/object out of another room/object's folder and into the default layout?

Not sure about the desktop editor; I can't use it as I don't have a Windows PC.

But on the web editor, it seems that the only way is to select the object you want to move, click 'Copy' in the top toolbar, go to the 'Objects' at the top of the left sidebar, hit 'Paste'. And then go back and delete the original, and rename your copy back to the name of the original.

It really is a pain that null doesn't show up in the 'Move' dialog.

In the "tree" view, just drag the room to a new location...
(drag and drop)