Arpeggio sequences + auto-start on first note

- Sequence mode: bars (2/4/6/8) with one chord per bar, chosen by
  functional rules (I->IV/V/vi...), diatonic cycle, or random (no immediate
  repeats); deterministic via melody seed. Chord symbols per bar in the
  score model (chordSymbols) rendered above the staff via setSection.
- Rhythm: quarters or eighths (cycling up/down through the pattern).
- Single-chord mode unchanged (whole path, overflow bars if needed).
- Auto-start: 'Start on first note (no count-in)' — step pace begins the
  run as soon as the mic detects the first note; no start press needed.
- 'New' button re-rolls the progression (new seed).
- Tests 174/174.

src/components/PhraseSheetMusic.tsx

@@ -272,6 +272,14 @@ export const PhraseSheetMusic: React.FC<PhraseSheetMusicProps> = ({
                     if (r === 0) treble.addTimeSignature(`${score.meter.numerator}/${score.meter.denominator}`);
                     treble.setMeasure(measure.number);
                 }
+                // Chord symbol above the staff (bar-indexed), drawn via the
+                // stave's annotation area so it shifts with the clef offset.
+                const chordSym = score.chordSymbols?.[m];
+                if (chordSym) {
+                    try {
+                        treble.setSection(chordSym, 0);
+                    } catch { /* courtesy label — never fatal */ }
+                }
                 let bass: Stave | null = null;
                 if (isGrand) {
                     bass = new Stave(x, y + 130, barWidth);