We are dealing with semantic difficulties here, imo. I don't have any problem with that underline statement above.
If you give me a synonym for what you take "author" to be and a synonym for what you take "design" to be, then I'll probably feel free to use those words. I simply don't see any difference in the statements "God is not the author of evil" and "God is not the designer of evil." I'm truly not trying to be difficult. I honestly don't see them being different.
I'll humor you and put it a different way: "Where did the 'system' (what it is, how it works...) of evil come from?"
Jean