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

DrumDetector.cs

@@ -17,11 +17,6 @@ public class DrumDetector
     readonly bool[] _subSnare = new bool[4];
     readonly bool[] _subBrass = new bool[4];
 
-    static readonly byte[] FreqKick = Freq.Compress4(new[] { 150, 150, 150, 150 });
-    static readonly byte[] FreqSnare = Freq.Compress4(new[] { 50, 50, 50, 50 });
-    static readonly byte[] FreqBrass = Freq.Compress4(new[] { 10, 10, 10, 10 });
-    static readonly byte[] FreqSilent = Freq.Compress4(new[] { 10, 10, 10, 10 });
-
     public void ProcessWindow(double[] magnitude, int sampleRate, int windowSize, int subTickIndex)
     {
         if (subTickIndex < 0 || subTickIndex > 3) return;
@@ -66,7 +61,7 @@ public class DrumDetector
     public WaveFrame BuildFrame()
     {
         var intensity = new byte[4];
-        var freqBytes = new byte[16]; // 4 sub-ticks × 4 bytes (but we use per-sub-tick freq)
+        var freqBytes = new byte[4];
 
         for (int i = 0; i < 4; i++)
         {