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/game/MatchTracker.test.ts

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+import { describe, it, expect } from 'vitest';
+import { MatchTracker } from './MatchTracker';
+
+const THRESHOLD = 50;
+const GRACE = 150;
+
+describe('MatchTracker', () => {
+    it('does not trigger before the threshold', () => {
+        const t = new MatchTracker(THRESHOLD, GRACE);
+        expect(t.update(true, 0)).toBe(false);
+        expect(t.update(true, 49)).toBe(false);
+    });
+
+    it('triggers once the threshold is reached', () => {
+        const t = new MatchTracker(THRESHOLD, GRACE);
+        expect(t.update(true, 0)).toBe(false);
+        expect(t.update(true, 50)).toBe(true);
+    });
+
+    it('triggers exactly once, then starts fresh', () => {
+        const t = new MatchTracker(THRESHOLD, GRACE);
+        t.update(true, 0);
+        expect(t.update(true, 60)).toBe(true);
+        // After triggering, tracker is reset: next frame must not re-trigger
+        expect(t.update(true, 70)).toBe(false);
+    });
+
+    it('survives a brief dropout within the grace period', () => {
+        const t = new MatchTracker(THRESHOLD, GRACE);
+        t.update(true, 0);          // start matching
+        t.update(false, 30);        // one flickered frame
+        expect(t.update(true, 60)).toBe(true); // 60ms elapsed > 50ms threshold
+    });
+
+    it('survives several short dropouts', () => {
+        const t = new MatchTracker(THRESHOLD, GRACE);
+        t.update(true, 0);
+        t.update(false, 16);
+        t.update(true, 32);
+        t.update(false, 48);
+        expect(t.update(true, 64)).toBe(true);
+    });
+
+    it('resets when the interruption exceeds the grace period', () => {
+        const t = new MatchTracker(THRESHOLD, GRACE);
+        t.update(true, 0);
+        t.update(false, 10);
+        // 200ms of silence later the user plays the note again:
+        // must NOT inherit the 200ms-old start time (that would fire instantly)
+        expect(t.update(true, 210)).toBe(false);
+        expect(t.update(true, 259)).toBe(false);
+        expect(t.update(true, 260)).toBe(true);
+    });
+
+    it('resets when a wrong note persists beyond grace', () => {
+        const t = new MatchTracker(THRESHOLD, GRACE);
+        t.update(true, 0);
+        t.update(false, 20);
+        t.update(false, 200);       // wrong note held: grace exceeded
+        expect(t.update(true, 210)).toBe(false); // restart from ~210
+        expect(t.update(true, 261)).toBe(true);
+    });
+
+    it('never triggers on non-matching frames alone', () => {
+        const t = new MatchTracker(THRESHOLD, GRACE);
+        expect(t.update(false, 0)).toBe(false);
+        expect(t.update(false, 1000)).toBe(false);
+    });
+
+    it('handles frames arriving long after the last one (throttled tab)', () => {
+        const t = new MatchTracker(THRESHOLD, GRACE);
+        // No frames for a while, then a single matching frame: fresh start.
+        expect(t.update(true, 5000)).toBe(false);
+    });
+
+    it('reset() clears accumulated progress', () => {
+        const t = new MatchTracker(THRESHOLD, GRACE);
+        t.update(true, 0);
+        t.update(true, 40);
+        t.reset();
+        expect(t.update(true, 50)).toBe(false); // restarted at 50
+        expect(t.update(true, 100)).toBe(true);
+    });
+});