Cleanup pass: remove dead code, fix bugs, simplify

Dead code removed:
- MusicAnalyzer.BuildWaveFrame (replaced by DrumDetector + BuildMelodyFrame)
- MusicAnalyzer.ExtractFeatures simplified to melody-only (removed rhythm band)
- MusicAnalyzer.RhythmLow/RhythmHigh constants, TickFeature.RhythmFlux
- LiveCapture._liveMaxFlux + _prevRhythmMag (computed, never read)
- State.ActualA/ActualB, State.LastSentA/LastSentB (set, never read)
- Program.cs StrengthChanged handler (only wrote to dead fields)
- Command.Mode property (never referenced)
- DrumDetector.FreqKick/Snare/Brass/Silent static arrays (unused)

Bugs fixed:
- DrumDetector.BuildFrame: freqBytes was byte[16], now byte[4]
- CoyoteDevice fallback: use nameFilter param instead of hardcoded string

Refactoring:
- Server.DoStatus calls BuildStatusPush(null) instead of duplicating
- HeatMap: removed redundant colW assignment
- Removed unused System.Numerics imports from LiveCapture, MusicAnalyzer

LiveCapture.cs

@@ -1,4 +1,3 @@
-using System.Numerics;
 using FftSharp;
 using NAudio.CoreAudioApi;
 using NAudio.Wave;
@@ -16,8 +15,6 @@ public class LiveCapture : IDisposable
     readonly Queue<double> _sampleBuffer = new();
     readonly object _bufferLock = new();
 
-    double[]? _prevRhythmMag;
-    double _liveMaxFlux;
     double _liveMaxMelodyEnergy;
     int _sampleRate;
     int _fftsPerTick;
@@ -131,13 +128,9 @@ public class LiveCapture : IDisposable
             var spectrum = FFT.Forward(windowData);
             var mag = FFT.Magnitude(spectrum);
 
-            var (rhythmEnergy, rhythmFlux, melodyEnergy, melodyFreq) =
-                MusicAnalyzer.ExtractFeatures(mag, _prevRhythmMag, _sampleRate);
-
-            _prevRhythmMag = mag;
+            var (melodyEnergy, melodyFreq) = MusicAnalyzer.ExtractFeatures(mag, _sampleRate);
 
             // Adaptive normalization: running max with slow decay
-            _liveMaxFlux = Math.Max(rhythmFlux, _liveMaxFlux * 0.999);
             _liveMaxMelodyEnergy = Math.Max(melodyEnergy, _liveMaxMelodyEnergy * 0.999);
 
             // Drum detection: map this FFT window to a sub-tick (0-3)