Unified target-note controls: key filter + fret window across all modes

- New shared PracticeFilter settings (keyTonic/keyMode/fretWindow), persisted
  via AppSettings.practice, defaults off (behavior unchanged).
- music/targetPool.ts: single source for the effective target pool —
  base playable range ∩ fret window ∩ key/mode pitch classes (9 modes incl.
  pentatonic, same scale machinery as Phrase Mode).
- useGameLogic now builds validNotes via computeTargetPool.
- TargetNoteControls component (key on/off + tonic/mode, fret window on/off +
  min/max) rendered in Controls for all game modes; key is independent of the
  displayed key signature.
- Phrase Mode binds its key/fret-window setup to the same shared filter
  (read/write mirror) and drops the duplicate controls in its setup panel.
- Tests: targetPool.test.ts (7 cases); suite 156/156 green, build ok.

src/music/targetPool.ts

@@ -0,0 +1,63 @@
+/**
+ * Unified target-note pool: base playable range (instrument + difficulty /
+ * fret window) intersected with the optional key-filter (pitch classes of a
+ * tonic+mode) and the optional fret window. Shared by all game modes so the
+ * controls behave identically everywhere.
+ */
+import { keyFor, type ModeId } from './scales';
+import { computePlayableNotes, fretWindowNotes, isFrettedInstrument } from './playableRange';
+import { TUNINGS } from './Tunings';
+
+export interface TargetPoolInput {
+    readonly instrumentId: string;
+    readonly difficulty: string;
+    readonly tuningId: string;
+    readonly customMinFret?: number;
+    readonly customMaxFret?: number;
+    /** Key filter (target-note key, independent of the displayed key signature). */
+    readonly keyEnabled: boolean;
+    readonly keyTonic: string;
+    readonly keyMode: string;
+    /** Fret window (fretted instruments only). */
+    readonly fretWindowEnabled: boolean;
+    readonly fretMin: number;
+    readonly fretMax: number;
+}
+
+/**
+ * Compute the effective target-note pool.
+ *
+ * Order of application:
+ *  1. base playable range (instrument difficulty / custom frets)
+ *  2. fret window (replaces the range for fretted instruments — same
+ *     semantics as Phrase Mode's fret window)
+ *  3. key filter (pitch-class intersection, keeps spelling/degree data intact
+ *     via the same scale machinery Phrase Mode uses)
+ */
+export function computeTargetPool(input: TargetPoolInput): number[] {
+    const tuning = TUNINGS[input.tuningId];
+    const fretted = isFrettedInstrument(input.instrumentId) && !!tuning;
+
+    // 1+2: base pool with optional fret window
+    let base: number[];
+    if (input.fretWindowEnabled && fretted) {
+        base = fretWindowNotes(tuning!, input.fretMin, input.fretMax);
+    } else {
+        base = computePlayableNotes({
+            instrumentId: input.instrumentId,
+            difficulty: input.difficulty,
+            tuningId: input.tuningId,
+            customMinFret: input.customMinFret,
+            customMaxFret: input.customMaxFret,
+        });
+    }
+    if (!input.keyEnabled) return base;
+
+    // 3: key/mode pitch-class filter
+    const mode: ModeId = (['major', 'minor', 'dorian', 'phrygian', 'lydian', 'mixolydian', 'locrian', 'major-pentatonic', 'minor-pentatonic'] as const).includes(input.keyMode as ModeId)
+        ? input.keyMode as ModeId
+        : 'major';
+    const key = keyFor(input.keyTonic, mode);
+    const pcs = new Set(key.pitchClasses);
+    return base.filter(midi => pcs.has(((midi % 12) + 12) % 12));
+}