vocab: stop re-teaching a word later in the same session (239 tags)

A word tagged VOCAB in one activity was tagged again in later activities of the
same session, so the learner got the same chip repeatedly — most visibly in the
pronunciation drills, which re-listed every word from the dialogue before them
(reported: book 7 session 1-2). Rule applied: drop a VOCAB whose word was
already tagged in an EARLIER activity of that session. Repeats INSIDE one
activity are kept — those teach distinct senses ('stuck to his finger' vs
'stuck the milk in the fridge', 'shop' as verb then noun). Also dropped chips
for plurals of already-known words in book 7 session 1-2, where the drill
teaches the singular/plural pair rather than new vocabulary. No session lost
all of its vocabulary (verified).

Co-authored-by: Cursor <cursoragent@cursor.com>

book-5-lesson-2.module

@@ -295,7 +295,6 @@ INTRO: Here's a picture of Dan at the barbershop. Listen to the new words in sen
 INSTRUCTION: Repeat each word and sentence.
 REPEAT
 
-VOCAB: barbershop
 LINE: Dan is at the barber shop. {page_037_001.jpg} {bk05-l2b-f1-01.mp3}
 
 VOCAB: hair
@@ -373,7 +372,6 @@ REPEAT
 
 LINE: Barbershop. {bk05-l2b-f2-01.mp3}
 LINE: Shampoo. {bk05-l2b-f2-02.mp3}
-VOCAB: haircut
 LINE: Haircut. {bk05-l2b-f2-03.mp3}
 VOCAB: to wash
 LINE: Washes. {bk05-l2b-f2-04.mp3}