feat(related): RelatedProgressions — loop-relative suggestions replace the generic table (task L-51)

KB-sourced ranking per the one-screen spec: same canonical degree
shape +100 (with the mandatory collapse of consecutive equal
degree/quality pairs — a real detector-produced 12-bar fires its blues
relatives despite the raw-index matcher bug), same style +40, shared
transitions +12 capped 36, degree-set Jaccard, length penalty; floor
24, max 5, never padded; entries render name/style/level/annotation +
the chord chain realized in the live key as real buttons ->
ChordDetailModal. match.js: additive exports only. Ride-along: dead
currentChord prop dropped from the banner mount. Critic PASS (both
hand-verified scores recomputed independently; full entry lists
byte-matched on three scenarios; collapse counterfactual = 39).

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

src/lib/match.js

@@ -91,7 +91,9 @@ export function findLoopPosition(chordHistory, loop) {
 // for each rotation, re-base so the first element is 0, then pick the
 // lexicographically smallest resulting sequence. Same loop → same string,
 // regardless of which chord it starts on.
-function canonicalDegrees(degrees) {
+// Exported additively for RelatedProgressions' ranking (task L-51,
+// one-screen.md §5) — no behaviour change.
+export function canonicalDegrees(degrees) {
   const n = degrees.length
   if (n === 0) return ''
   let best = null
@@ -110,7 +112,9 @@ function canonicalDegrees(degrees) {
 
 // Converts a loop of chord-name strings into semitone offsets from the loop's
 // own first chord. Returns null if any chord root is unparseable.
-function loopToDegrees(loop) {
+// Exported additively for RelatedProgressions' ranking (task L-51,
+// one-screen.md §5) — no behaviour change.
+export function loopToDegrees(loop) {
   if (!loop?.length) return null
   const pcs = loop.map(chordRootPC)
   if (pcs.some(pc => pc < 0)) return null