stable session ids: prefix the 3 unprefixed $LESSON titles (book-11 dup 'Dialogues and Comprehension' collided across files and broke the manifest join); repair book-11-lesson-1 session headers polluted by the earlier activity rebuild (source-file $LESSON lines had leaked in)

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

book-11-lesson-1.module

@@ -1118,7 +1118,7 @@ ANSWER: f
 FEEDBACK: Side 4 is 3 inches long. {bk11-l1c-f2-01p.mp3}
 
 
-$LESSON The Present Perfect Tense
+$LESSON 1-7: The Present Perfect
 
 # Source: ST §The Present Perfect Tense
 
@@ -1352,7 +1352,6 @@ PROMPT: Has he been home since Thursday evening? {bk11-l1c-f7-01k.mp3}
 RESPONSE: Yes, he's been home since 6:45 Thursday evening. {bk11-l1c-f7-01l.mp3}
 
 
-$LESSON How Long?
 
 # Source: ST §Answer with the Present Perfect
 
@@ -1544,7 +1543,6 @@ PROMPT: Doug has a problem with math. {bk11-l1c-f9-01q.mp3}
 RESPONSE: How long has he had a problem with math? {bk11-l1c-f9-01r.mp3}
 
 
-$LESSON Listening Skills
 
 # Source: ST §How Long Will You Be There?