Should I be credited for my programming contribution to a dissertation?
You did work for hire for a research group. Since you say you were strictly involved in developing the tool and not in the research, authorship of subsequent publications is not to be expected. An acknowledgment in the thesis would be appropriate but it would have very little weight in a CV, inside or outside academia.

At any rate, you can definitely list your contribution to this project in your CV regardless of which kind of acknowledgment you might get. In fact having delivered a working software and gotten paid for it will be much more helpful than any kind of authorship/acknowledgments when applying for jobs outside academia.