This was great! I love how it feels like origami, very relaxing.
I think the UX could be a bit better in places, it can be very fiddly. Even though you can submit off-rotation solutions, it can hurt visualization to do it that way, so it would be nice to be able to rotate the whole thing at once. It can also be awkward when you want to rotate a piece a certain way, but can't because the other pieces are colliding; something which pushes pieces around their pivots to allow the user's rotation to happen could be really nice. It's also a bit fiddly to have to tap the pivot, then drag the shape, especially when a piece only has one pivot, but outside of that case I'm not sure what the best UX would be
But yes, I really really liked this, great job all!