I have never felt that a design was included in the idea of a full-stack software engineer. that would be something id mention separately if I had the skill.
But I do agree with you that on job descriptions, "full-stack" tends to stop at javascript.
The nice thing is nowadays Bootstrap (maybe with a decent theme like Flat UI or Ace Admin) will get you 90% of the way there. Very basic design knowledge will get you the other 10%, and for anything past that you can hire a designer.