feat(kb): jazz piano cell — the KB's first authored piano pack (task P-22)

14 plays (7 progressions x 2): Bud Powell shells, rootless Type A/B,
guide-tone comps; comping rhythms; piano-angled improv. Hand spans
<= a 10th throughout. Critic returned once (6 prose voice-leading
overclaims on fifths-apart dominant alternation), fixed, PASS on
re-gate (all 6 corrected sentences arithmetic-verified both
directions); ride-along one-word polish per gate suggestion.
Rendering the authored pack in the Jam Guide is task L-24.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/data/kb/index.js

@@ -3,6 +3,7 @@
 import jazzMeta from './jazz/meta.js'
 import jazzProgressions from './jazz/progressions.js'
 import jazzGuitar from './jazz/guitar.js'
+import jazzPiano from './jazz/piano.js'
 import bluesMeta from './blues/meta.js'
 import bluesProgressions from './blues/progressions.js'
 import bluesGuitar from './blues/guitar.js'
@@ -35,7 +36,7 @@ export default {
   jazz: {
     meta: jazzMeta,
     progressions: jazzProgressions,
-    instruments: { guitar: jazzGuitar },
+    instruments: { guitar: jazzGuitar, piano: jazzPiano },
   },
   blues: {
     meta: bluesMeta,