Add drum detection for channel A in live capture

- DrumDetector.cs: 3-band onset detection (kick/snare/brass) with adaptive
  thresholds, per-sub-tick timing within 100ms frames
- Kick: low-band onset, 150ms deep thump
- Snare: broadband (mid+high) onset, 50ms mid punch
- Brass: high-only onset, 10ms buzzy
- Priority: kick > snare > brass when multiple hit same sub-tick
- Intensity = max (100) on hit, 0 on silence — user limiter scales down
- MusicAnalyzer: add BuildMelodyFrame for chB only (pitch+energy)
- LiveCapture: chA now from DrumDetector, chB unchanged (melody)
- Sub-tick mapping: FFT window position → 0-3 within each 100ms tick

LiveCapture.cs

@@ -22,6 +22,7 @@ public class LiveCapture : IDisposable
     int _sampleRate;
     int _fftsPerTick;
     int _fftIndexInTick;
+    readonly DrumDetector _drums = new();
 
     public event Action? Stopped;
 
@@ -139,7 +140,12 @@ public class LiveCapture : IDisposable
             _liveMaxFlux = Math.Max(rhythmFlux, _liveMaxFlux * 0.999);
             _liveMaxMelodyEnergy = Math.Max(melodyEnergy, _liveMaxMelodyEnergy * 0.999);
 
-            tf.RhythmFlux = Math.Max(tf.RhythmFlux, rhythmFlux);
+            // Drum detection: map this FFT window to a sub-tick (0-3)
+            int subTick = _fftsPerTick > 0 ? _fftIndexInTick * 4 / _fftsPerTick : 0;
+            if (subTick > 3) subTick = 3;
+            _drums.ProcessWindow(mag, _sampleRate, MusicAnalyzer.WindowSize, subTick);
+
+            // Melody accumulation for chB
             tf.MelodyEnergy += melodyEnergy;
             tf.MelodyFreqSamples.Add(melodyFreq);
             tf.MelodyCount++;
@@ -147,7 +153,8 @@ public class LiveCapture : IDisposable
 
             if (_fftIndexInTick >= _fftsPerTick)
             {
-                var (frameA, frameB) = MusicAnalyzer.BuildWaveFrame(tf, _liveMaxFlux, _liveMaxMelodyEnergy);
+                var frameA = _drums.BuildFrame();
+                var frameB = MusicAnalyzer.BuildMelodyFrame(tf, _liveMaxMelodyEnergy);
                 _state.EnqueueStream('A', new[] { frameA });
                 _state.EnqueueStream('B', new[] { frameB });