I wouldn't tell them anything at all, for starters.

But if I were for some reason obligated to say something, I might write a note along the lines of 'Very minor magical talent, wholly unremarkable.' You cannot say 'Magical talent, unspecified'! The reader will imagine all sorts of dramatic things! And when it goes in combination with what you have already written and sent of me—that I'm highly clever and have a keen eye for design—

[Are those the words he'd used? Close enough.]

—then I will seem highly formidable indeed. I can't imagine your masters are in the business of letting formidable persons simply do as they please. Particularly not once the war has ended.