How to disagree about author order when my advisor has been dismissive of such concerns in the past?
Depending on your field, it may be possible to submit your paper to a journal which allows for "co-equal first authors": that is, both the first and second are treated equally as first authors within the journal. You could then mention this in your CV. That way, I don't think there's much harm done; this would represent the path of least resistance.

Otherwise, you're going to have to be willing to involve someone to deal with this issue—whether it's your advisor, the dean, or other professors in the department. There's no way to resolve this issue without it. (I presume you mean the chair of your department, or other similar official, when you use the term "dean.") But the first step should be to talk with your advisor, before the paper is written. You may be able to clarify things at that stage. I'd involve the other members of your thesis committee (if you have one), and then finally work with the dean.