Export interface with interactive option

[jrmoynihan]

Cool library! I'm hoping it will solve the use-case for my side-project: Nested interactive elements -- a re-orderable wiki tree, essentially. Could be a good example to add for your readme?

However, it seems that the public API doesn't surface the interactive option. Should probably use the same interface in the action ($lib/actions/draggable.ts) and the public API ($lib/types/index.ts) and re-export it rather than extending he base interface inside the action.