Update 05
I wrote a very simple rotation system today, which doesn't actually rotate anything - all the block sprites remain at the same angle, but the component blocks of the tetromino are rearranged around whichever block you click. I've done it this way because a) if the block sprites are going to have shapes on them so that colourblind people can read them better, they ought to look consistent no matter how the tetromino is rotated; b) I'm using the top-left corner of each sprite to align it to the grid, which is more intuitive to me than using the center, and rotating the sprite might mess with this; and c) doing it properly with vectors sounds like hard work.
Unfortunately, this simple system didn't work at first, so most of my effort today has gone into troubleshooting about seven lines of code for two hours. It always turns out to be some silly mistake I forgot when I have trouble with coding. As it turns out, my rotation code works perfectly (as far as I know), but it was being overruled instantly by the code which keeps blocks together while the mouse is carrying them around.
So here's what Puzzle Wizard looks like now:
As you can see, I'm thinking about how the game is going to be laid out now. I'm not happy with this yet, but I like the target shape being right in the centre. (I think each enemy type will have its own unique shape, though I probably won't get to make many enemy types before time is up.) Please excuse the placeholder boxes, they look much uglier than I expected.
(I've also made the target shape slightly larger than the grid - I think that little white border around a full target shape looks really good.)