Fix missing 'baa' variable in NURSERY_PIECES causing all genres to disappear

The NURSERY_PIECES IIFE referenced 'baa' (Baa Baa Black Sheep) in its return
array but the variable was never defined — it was lost during the Prime genre
merge. This ReferenceError crashed the script on load, preventing all genre
tabs and rhythm lists from rendering.

https://claude.ai/code/session_01MhCcEPfX3JqAk8zmvLXZ1g

index.html

@@ -4118,6 +4118,12 @@ const NURSERY_PIECES=(function(){
     [2,3,0,3,1,2,1,2,1,2,1,0,2,3,0,3,1,2,1,0],
     [1,1,2,1,1,1,2,1,1,1,1,2,1,1,2,1,1,1,1,4],
     3,C4);
+  // ── Baa Baa Black Sheep (same melody as Twinkle Twinkle) ──
+  var baa=rhyme("Baa Baa Black Sheep","English (1731)",80,
+    [C4,C4,G4,G4,A4,A4,A4,G4,F4,F4,E4,E4,D4,D4,C4,G4,G4,G4,F4,F4,F4,E4,E4,E4,D4,D4,D4,C4],
+    [0,0,3,3,0,0,0,3,1,1,2,2,1,1,0,3,3,3,1,1,1,2,2,2,1,1,1,0],
+    [1,1,1,1,1,1,1,3,1,1,1,1,1,1,3,1,1,1,1,1,1,1,1,1,1,1,1,4],
+    3,C4);
   // ── Classics (from Prime, simple versions) ──
   var twinkle=rhyme("Twinkle Twinkle Little Star","Traditional (1760s)",75,
     [C4,C4,G4,G4,A4,A4,G4,F4,F4,E4,E4,D4,D4,C4,G4,G4,F4,F4,E4,E4,D4,C4,C4,G4,G4,A4,A4,G4,F4,F4,E4,E4,D4,D4,C4],