Accidentally omitted salt from my gingerbread cookies... what should I do?
Salt is primarily a flavor enhancer in cookies. It's unlikely that omitting it will affect the recipe greatly. I know people who regularly omit salt with no problems. 

Bake the cookies! Don't waste the ingredients. You probably won't notice a huge change in flavor. 

As a note, you're unlikely to get an even incorporation adding it at this point, so don't try that. You'll either end up with tough dough from overworking it or salty pockets if you don't.