fix: asymmetric meter decay for faster desktop level response

Issue 3: Desktop meter now decays 2.5x faster than it rises
(DecaySmoothing=0.5 vs Smoothing=0.2). When rms drops below current
level the higher alpha pulls the bar down quickly; when audio returns
it rises smoothly. 207 tests pass, 0 warnings.

Services/Audio/AudioLevelMeter.cs

@@ -9,6 +9,7 @@ namespace ytLive.Services.Audio;
 public sealed class AudioLevelMeter
 {
     private const float Smoothing = 0.2f;
+    private const float DecaySmoothing = 0.5f;
     private float _level;
 
     public float Level => _level;
@@ -44,7 +45,8 @@ public sealed class AudioLevelMeter
         }
 
         var rms = (float)Math.Sqrt(sumSquares / count);
-        _level = _level * (1 - Smoothing) + rms * Smoothing;
+        var alpha = rms > _level ? Smoothing : DecaySmoothing;
+        _level = _level * (1 - alpha) + rms * alpha;
         return _level;
     }