You're absolutely free to distribute anything you make with Decker as you please, including selling your programs if you wish.
Submissions to Decktember should provide a free web-playable version, but there's nothing stopping you from making your submission a demo of a larger game or continuing to work on your project after the jam release.
Providing links to the Decker page is not required, but always appreciated. I rely entirely upon word-of-mouth to help other people find out about Decker.