Phase 4: drone + T6/E-series + polish + deploy + README

Add drone synth + DronePlayer, wire T6 (mode over drone) and E1-E3 info pages
(E3 carries a drone). Screen Wake Lock while any click/drone plays. Vitest suite
for scheduler timing (no drift over 5 min) and music-layer correctness (triads,
CAGED, diatonic, fretboard). Deploy artifacts: public/_redirects, multi-stage
Dockerfile + nginx.conf (SPA fallback, immutable asset caching, gzip),
.dockerignore. README covering build, Cloudflare Pages / nginx / Docker deploy,
and the deep-link URL format. prefers-reduced-motion honored throughout.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lib/music/music.test.ts

@@ -0,0 +1,67 @@
+import { describe, it, expect } from 'vitest'
+import { chromaAt, pcAt } from './fretboard'
+import { triadNotes, diatonicChords, scaleNotes, intervalTarget } from './theory'
+import { triadShape, STRING_SETS } from './triads'
+import { cagedShapes } from './caged'
+import { deriveRoles } from '../../drills'
+
+describe('fretboard mapping', () => {
+  it('maps open strings and frets correctly (index 0 = high e)', () => {
+    expect(pcAt(0, 0)).toBe('E') // high e open
+    expect(pcAt(5, 0)).toBe('E') // low E open
+    expect(pcAt(5, 3)).toBe('G') // low E, 3rd fret
+    expect(pcAt(4, 2)).toBe('B') // A string, 2nd fret
+    expect(chromaAt(0, 0)).toBe(4) // E
+  })
+})
+
+describe('theory helpers', () => {
+  it('builds triads and diatonic chords', () => {
+    expect(triadNotes('C', 'major')).toEqual(['C', 'E', 'G'])
+    expect(triadNotes('A', 'minor')).toEqual(['A', 'C', 'E'])
+    expect(diatonicChords('G').map((c) => c.name)).toEqual([
+      'G', 'Am', 'Bm', 'C', 'D', 'Em', 'F#dim',
+    ])
+    expect(scaleNotes('G', 'dorian')).toEqual(['G', 'A', 'Bb', 'C', 'D', 'E', 'F'])
+    expect(intervalTarget('A', '5P')).toBe('E')
+  })
+})
+
+describe('deriveRoles', () => {
+  it('accents, downbeats, and subdivisions land correctly', () => {
+    // 4/4 sixteenths, accent on beat 1.
+    const roles = deriveRoles(16, 4, [0])
+    expect(roles[0]).toBe('accent')
+    expect(roles[4]).toBe('normal') // beat 2 downbeat
+    expect(roles[1]).toBe('subdivision')
+  })
+})
+
+describe('triad inversions', () => {
+  it('produces C major tones on the 1-2-3 string set', () => {
+    const set = STRING_SETS.find((s) => s.id === '123')!
+    for (const inv of ['root', '1st', '2nd']) {
+      const shape = triadShape('C', 'major', set, inv)
+      const chromas = shape.frets
+        .map((f, string) => (f >= 0 ? chromaAt(string, f) : null))
+        .filter((c): c is number => c !== null)
+        .sort((a, b) => a - b)
+      // C(0) E(4) G(7)
+      expect(chromas).toEqual([0, 4, 7])
+    }
+  })
+})
+
+describe('CAGED shapes', () => {
+  it('returns 5 shapes with the E-shape barre at fret 3 for key G', () => {
+    const shapes = cagedShapes('G')
+    expect(shapes).toHaveLength(5)
+    const eShape = shapes.find((s) => s.form === 'E shape')!
+    expect(eShape.barreFret).toBe(3)
+    // Every marked position should be a chord tone of G major (G B D).
+    const gTones = new Set([7, 11, 2])
+    for (const p of shapes[0].positions) {
+      expect(gTones.has(chromaAt(p.string, p.fret))).toBe(true)
+    }
+  })
+})