Arpeggio material for Phrase Mode (variant 1)

- music/arpeggioGenerator.ts: diatonic triads (I-vii*) built from the
  selected key/mode via the shared degree spelling; patterns up / down /
  up-down / 1-2-3-5; one or two octaves (cycle ends on the octave; two-
  octave path continues from the turning root). Quarter-note rhythm with
  final note extended to fill the bar; title is labeled 'Arpeggio -
  <tonic> <degree> (pattern, coverage)'.
- Settings: PhraseMaterial 'arpeggio' + arpeggioDegree/Pattern/Coverage
  (defaults I / up / one-octave).
- PhraseTrainer: material option 'Arpeggios (generated)' + Chord/Pattern/
  Coverage/Meter selects; key/mode reuse the shared Target key controls.
- Tests: 9 arpeggio cases (170 total).

src/types/SettingsTypes.ts

@@ -39,7 +39,7 @@ export interface RhythmSettings {
     volume: number;
 }
 
-export type PhraseMaterial = 'melody' | 'scale' | 'library' | 'import';
+export type PhraseMaterial = 'melody' | 'scale' | 'arpeggio' | 'library' | 'import';
 export type PhrasePace = 'step' | 'tempo';
 
 export interface PhraseSettings {
@@ -53,6 +53,10 @@ export interface PhraseSettings {
     rhythmLevel: 1 | 2 | 3;
     scaleCoverage: 'one-octave' | 'two-octave' | 'position';
     scaleDirection: 'up' | 'down' | 'updown';
+    /** Arpeggio settings (material = 'arpeggio'). */
+    arpeggioDegree: string; // ArpeggioDegree
+    arpeggioPattern: 'up' | 'down' | 'updown' | '1235';
+    arpeggioCoverage: 'one-octave' | 'two-octave';
     /** Phrase-local fret window (guitar/bass) — overrides the note set. */
     fretWindowEnabled: boolean;
     fretMin: number;
@@ -79,6 +83,9 @@ export const DEFAULT_PHRASE_SETTINGS: PhraseSettings = {
     rhythmLevel: 1,
     scaleCoverage: 'one-octave',
     scaleDirection: 'updown',
+    arpeggioDegree: 'I',
+    arpeggioPattern: 'up',
+    arpeggioCoverage: 'one-octave',
     fretWindowEnabled: false,
     fretMin: 0,
     fretMax: 4,