feat: guitar voicing templates

app/app/lib/guitar-voicings.ts

@@ -0,0 +1,88 @@
+export interface GuitarVoicingTemplate {
+  /** 6 strings low→high; 0 = root position, 1 = one fret above root, null = muted */
+  frets: (number | null)[];
+  /** Fret (0-based relative) where a full barre is drawn, or null */
+  barre: number | null;
+  /** Which open string carries the root — determines transposition offset */
+  rootString: 'E' | 'A';
+}
+
+/**
+ * Moveable barre-chord templates keyed by tonal chord type name.
+ * Verified fingerings at root = E (E-shape) or root = A (A-shape).
+ * To add a new quality: look up `Chord.get('<example>').type` in tonal,
+ * then define the fingering at root E or A and add it here.
+ */
+export const GUITAR_VOICINGS: Record<string, GuitarVoicingTemplate> = {
+  // ── E-shape (root on 6th string) ──────────────────────────────────────
+  // E major open: [0,2,2,1,0,0]  E B E G# B E
+  'major': {
+    frets: [0, 2, 2, 1, 0, 0],
+    barre: null,
+    rootString: 'E',
+  },
+  // E7: [0,2,0,1,0,0]  E B D G# B E
+  'dominant seventh': {
+    frets: [0, 2, 0, 1, 0, 0],
+    barre: null,
+    rootString: 'E',
+  },
+  // Emaj7: [0,2,1,1,0,0]  E B D# G# B E
+  'major seventh': {
+    frets: [0, 2, 1, 1, 0, 0],
+    barre: null,
+    rootString: 'E',
+  },
+  // Eaug: [0,3,2,1,1,0]  E C(=B#) E G# C E
+  'augmented': {
+    frets: [0, 3, 2, 1, 1, 0],
+    barre: null,
+    rootString: 'E',
+  },
+  // Esus4: [0,2,2,2,0,0]  E B E A B E
+  'suspended fourth': {
+    frets: [0, 2, 2, 2, 0, 0],
+    barre: null,
+    rootString: 'E',
+  },
+
+  // ── A-shape (root on 5th string) ──────────────────────────────────────
+  // Am open: [x,0,2,2,1,0]  A E A C E
+  // barre: 0 so that transposed versions (Bm, Cm, etc.) draw the barre bar;
+  // the renderer suppresses the barre when baseFret===0 (open position = no barre needed)
+  'minor': {
+    frets: [null, 0, 2, 2, 1, 0],
+    barre: 0,
+    rootString: 'A',
+  },
+  // Am7: [x,0,2,0,1,0]  A E G C E
+  'minor seventh': {
+    frets: [null, 0, 2, 0, 1, 0],
+    barre: null,
+    rootString: 'A',
+  },
+  // AmMaj7: [x,0,2,1,1,0]  A E G# C E
+  'minor major seventh': {
+    frets: [null, 0, 2, 1, 1, 0],
+    barre: null,
+    rootString: 'A',
+  },
+  // Adim: [x,0,1,2,1,x]  A Eb A C (string 1 muted)
+  'diminished': {
+    frets: [null, 0, 1, 2, 1, null],
+    barre: null,
+    rootString: 'A',
+  },
+  // Am7b5 (half-dim): [x,0,1,0,1,x]  A Eb G C
+  'half-diminished': {
+    frets: [null, 0, 1, 0, 1, null],
+    barre: null,
+    rootString: 'A',
+  },
+  // Asus2: [x,0,2,2,0,0]  A E A B E
+  'suspended second': {
+    frets: [null, 0, 2, 2, 0, 0],
+    barre: null,
+    rootString: 'A',
+  },
+};