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

MusicAnalyzer.cs

@@ -79,6 +79,33 @@ public static class MusicAnalyzer
         public readonly List<double> MelodyFreqSamples = new();
     }
 
+    public static WaveFrame BuildMelodyFrame(TickFeature tf, double maxMelodyEnergy)
+    {
+        double avgEnergy = tf.MelodyCount > 0 ? tf.MelodyEnergy / tf.MelodyCount : 0;
+        double normalizedEnergy = maxMelodyEnergy > 0 ? avgEnergy / maxMelodyEnergy : 0;
+        int melodyIntensity = (int)Math.Round(normalizedEnergy * 80);
+        melodyIntensity = Math.Clamp(melodyIntensity, 0, 100);
+
+        double weightedFreq = 0;
+        double totalWeight = 0;
+        foreach (var f in tf.MelodyFreqSamples)
+        {
+            weightedFreq += f * f;
+            totalWeight += f;
+        }
+        double avgMelodyHz = totalWeight > 0 ? weightedFreq / totalWeight : 500;
+        int estimsMs = MapPitchToPeriod(avgMelodyHz);
+
+        var intB = new[]
+        {
+            (byte)melodyIntensity, (byte)melodyIntensity,
+            (byte)melodyIntensity, (byte)melodyIntensity
+        };
+        var freqB = Freq.Compress4(new[] { estimsMs, estimsMs, estimsMs, estimsMs });
+
+        return new WaveFrame(freqB, intB);
+    }
+
     public static (WaveFrame chA, WaveFrame chB) BuildWaveFrame(TickFeature tf, double maxFlux, double maxMelodyEnergy)
     {
         const int rhythmFreqMs = 150;