kb: add rock guitar pack; schema gains declared omit3 (power chords)

5 progressions (Mixolydian vamp, I-IV-V, minor descent, axis, Dorian
riff cell) x 2 plays: open-chord Malcolm hits, second-guitar triads,
Keith sus figure, power-chord chug, Police add9 arpeggios, thumb-over
embellishments. omit3 is a declared omission like rootless - the
pitch-class check still applies. Validator and build green.

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

src/data/kb/rock/meta.js

@@ -0,0 +1,7 @@
+export default {
+  id: 'rock',
+  label: 'Rock',
+  feel: 'straight',
+  tempoRange: [80, 180],
+  character: 'Straight eighths, big chords, and arrangement-as-dynamics: the same progression whispered in the verse and detonated in the chorus.',
+}