Sorry. Were I to send them a script and concept art, how would they respond?

Sadly, they would not. DC does not accept unsolicited manuscripts.

You could show your concept art to an editor at a convention portfolio review, I imagine, but I think your likelihood of a positive result is tiny.

Almost no one breaks in to DC or Marvel with no former comics experience, particularly on a mini (which means it has to be sold to retailers based on SOMETHING and new creators have no name for the retailers to order by) or on a bat-related book (which is kind of Advanced Comics Writing as far as freelancers go).

Your best bet is to get some comics work published elsewhere and give that to editors. That has a decent chance of catching their attention.