Lemma: Read math textbooks like code

hi PH! i made lemma while working through ESL, mostly because i kept losing my place flipping back to "see (3.41)" and "by theorem 2.3". it reads the pdf once on your mac and turns those references into links. hover to preview, click to see the statement right under the line you're on. proofs fold, and when a book says "it is easy to show" you can write the steps and each line gets checked (a sign slip comes back as a counterexample). it's mac only (macOS 15+) and not notarized yet, so macOS asks you to allow it once. it still misses on some pdfs (scans, odd numbering). if you try it on the book you're reading, tell me where it gets things wrong. it's GPL, and there are good first issues if you'd rather fix it yourself.