feat(kb): intermediate progressions + level tags for jazz, gospel, rnb (task P-20)

6 new level:'intermediate' progressions (tritone sub, rhythm-changes
bridge, gospel passing-dim walk-up, tonicized amen w/ borrowed iv,
Just-the-Two-of-Us loop, Sir Duke chromatic vi) x 2 guitar plays each;
all progressions in the three styles now carry explicit level. KB:
56 progressions / 112 plays. Critic returned once (3 caption theory
misstatements), fixed, PASS on re-gate (voice-leading arithmetic
hand-verified from shape constants).

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

src/data/kb/rnb/progressions.js

@@ -1,3 +1,11 @@
+// Level tags + the two intermediate progressions added by task P-20.
+// Intermediate-entry changes verified against: guitarmusictheory.com &
+// Hooktheory TheoryTab & musescore.com feature ("Just the Two of Us" —
+// D♭maj7–C7–Fm7 with the E♭m7–A♭7 ii–V pointing back at ♭VI, key of F minor),
+// Hooktheory TheoryTab & songdna.blogspot.com & spytunes.com ("Sir Duke"
+// verse B–G♯m–G–F♯7 = I–vi–♭VI7–V chromatic descent),
+// docs/progression-repertoire.md §2 (modal interchange, secondary dominants,
+// tritone substitution rows).
 export default [
   {
     id: 'rnb-mediant-circle',
@@ -9,6 +17,7 @@ export default [
     mode: 'major',
     songs: ['September — Earth, Wind & Fire (rotation family)', 'the soul turnaround started from the iii'],
     tip: 'The 1-6-2-5 family entered from the mediant — home is implied for three bars before the V finally points at it. Neo-soul lives in that deferral.',
+    level: 'foundation',
   },
   {
     id: 'rnb-6251',
@@ -20,6 +29,7 @@ export default [
     mode: 'major',
     songs: ["Isn't She Lovely — Stevie Wonder"],
     tip: 'The II is a secondary dominant (not the polite ii), and the V arrives as a 9sus — suspended, never quite dominant, melting into the I. Stevie\'s whole cadence language in four chords.',
+    level: 'intermediate',
   },
   {
     id: 'rnb-maj7-vamp',
@@ -31,6 +41,7 @@ export default [
     mode: 'major',
     songs: ['Waiting in Vain — Bob Marley', "Cruisin' — Smokey Robinson (I–ii7 variant)"],
     tip: 'Two lush chords trading forever — the song is the texture. The same vamp underpins half of modern bedroom R&B; colour it differently every two bars.',
+    level: 'foundation',
   },
   {
     id: 'rnb-dorian',
@@ -42,6 +53,7 @@ export default [
     mode: 'dorian',
     songs: ["Spanish Joint — D'Angelo", "Didn't Cha Know — Erykah Badu (i–iv minor variant)", "Brown Sugar — D'Angelo (E Dorian loop)"],
     tip: 'The IV9 carries the raised 6th that makes it Dorian — the same pair as the funk vamp, slowed to 70 BPM and dragged behind the beat.',
+    level: 'foundation',
   },
   {
     id: 'rnb-gospel-amen',
@@ -53,5 +65,30 @@ export default [
     mode: 'major',
     songs: ['the gospel "Amen" cadence', 'countless soul ballad turnarounds (borrowed iv)'],
     tip: 'The IV turns minor on its way home — borrowed from the parallel minor, the single most-borrowed chord in soul. One semitone (the 3rd of the IV falling) does all the work.',
+    level: 'intermediate',
+  },
+  {
+    id: 'rnb-justthetwo',
+    name: 'Just-the-Two-of-Us loop (♭VI–V–i + ii–V of ♭VI)',
+    rn: ['♭VImaj7', 'V7', 'i7', '♭vii7', '♭III7'],
+    degrees: [8, 7, 0, 10, 3],
+    qualities: ['maj7', 'dom7', 'min7', 'min7', 'dom7'],
+    bars: [1, 1, 2, 1, 1],
+    mode: 'minor',
+    songs: ['Just the Two of Us — Grover Washington Jr. & Bill Withers', 'a smooth-soul/90s-R&B staple loop'],
+    tip: 'A minor loop that spends most of its time away from home: ♭VI–V–i falls in half steps, then the ♭vii–♭III7 is a ii–V aimed back at ♭VI, not at i. Hearing ii–Vs that target chords other than the tonic is the door out of diatonic playing — in the original the last two chords share one bar.',
+    level: 'intermediate',
+  },
+  {
+    id: 'rnb-chromatic-vi',
+    name: 'Chromatic soul descent (I–vi–♭VI7–V)',
+    rn: ['I', 'vi7', '♭VI7', 'V7'],
+    degrees: [0, 9, 8, 7],
+    qualities: ['maj', 'min7', 'dom7', 'dom7'],
+    bars: [1, 1, 1, 1],
+    mode: 'major',
+    songs: ['Sir Duke — Stevie Wonder (verse)'],
+    tip: 'One swapped chord makes it: where the diatonic loop would repeat vi or move to IV, the ♭VI7 (borrowed from the parallel minor) slides the bass down 6–♭6–5 in half steps. It doubles as a tritone sub of II7 (V/V) — either way the whole chord planes down a semitone into V.',
+    level: 'intermediate',
   },
 ]