I think this is a case where Profession =/= Skill.
There can be many skills that together make a profession. In this case, I think the main skills are those you already mentioned: craftsmanship and performance. Craftsmanship would be the actual creating of the jewelery, while performance would be (among other things) the design part. You could, of course, switch one of those over to the other with a stunt, if you don't want to take both skills at a high level. Depending on if you want to be more artsy or more crafty, you choose the skill you switch over.
Then again, it also depends on what you want it to do in the game. If it is "just" to make your personalized jewelery focus items, I could see 2 ways to go. Either that is totally in the narrative, you are a goldsmith wizard, and so you make your stuff. There isn't really a roll involved in doing it, and since craftsmanship isn't relevant to your character otherwise, you don't have a high skill there (while still being a good goldsmith). Or you use Craftsmanship/Performance instead of Lore when determining the power of enchanted and focus items, again determined by if you are more artsy or crafty. I wouldn't even make you take a stunt for it, you are not really better off by splitting your wizard trio of skills into a wizard quartet.
If you want to have a well running jewelery store in your background, a high resources skill would work as well. You don't play out the day to day, you just have a reasonable amount of money, as well as materials like gold, silver and gemstones at your disposal, the amount determined by your resources skill. Other skills wouldn't have to play into this, if you don't want to do other things as well.