Overhaul pitch detection and note matching

- Pick detector per instrument range: ACF2PLUS (robust down to ~40 Hz) for
  normal instruments, YIN only for the whistle register. pitchfinder's YIN
  latches onto tau=2 (~20 kHz garbage) below ~100 Hz and for quiet input;
  the old fixed 4096 window masked this, the smaller window exposed it.
- RMS-normalize analysis input for the YIN path only; ACF2PLUS keeps the raw
  signal so its internal unpitched gate rejects quiet decayed audio instead
  of amplifying noise into confident wrong pitches (tuner stuck on 'a note').
- Adaptive analysis window sized to the instrument's lowest note (~2 periods):
  half the latency, a quarter of the CPU for guitar/piano/voice; bass keeps
  the full window for E1.
- Reject detections implausibly below the instrument floor (mains hum).
- Clear stale pitch readings after 200 ms instead of keeping them forever.
- Shared AudioEngine singleton for all playback (was: two AudioContexts);
  tracks audibility so the app stops hearing its own speaker (ear-training
  self-scoring) and gates matching plus display during playback.
- MatchTracker: grace-period based note hold instead of reset-on-every-flicker
  (YIN flickers during attacks/decays; the old hard reset made the 50 ms
  threshold fire unreliably).
- Display damping in the producer (EMA for cents/level, 3-frame note-name
  hysteresis); display components render directly without CSS transitions.
- Regression tests: synthetic signals through the exact pipeline helpers
  (MatchTracker + pitchDetection test suites).

src/types/SettingsTypes.ts

@@ -25,6 +25,11 @@ export interface AppSettings {
     customMaxFret?: number;
     autoPlaySightReading?: boolean;
     autoPlayVolume?: number;
+    /** Length of the played reference note in seconds */
+    referenceNoteDuration?: number;
+    /** Hold the next reference note until the microphone detects silence,
+     *  so a still-ringing instrument doesn't mask it */
+    waitForQuiet?: boolean;
     virtualGuitarVolume?: number;
     virtualGuitarMute?: boolean;
     micSensitivity?: number;
@@ -55,6 +60,8 @@ export const DEFAULT_SETTINGS: AppSettings = {
     customMaxFret: 12,
     autoPlaySightReading: false,
     autoPlayVolume: 0.5,
+    referenceNoteDuration: 1.5,
+    waitForQuiet: false,
     virtualGuitarVolume: 0.5,
     virtualGuitarMute: false,
     micSensitivity: 0.5,