Added a firm guide rule: drop a cassette activity ONLY to dissolve a
bare word-list or remove a true duplicate; keep every other. This cut
over-dropping sharply (book-4-lesson-3: 83 -> 6 dropped clips, all the
sanctioned word-list; book-1-lesson-2: 49 -> 22). Generated the Book-1
review ST images so book-1-lesson-5 can ship. All 10 masters now live.
Co-authored-by: Cursor <cursoragent@cursor.com>
