fix(dock): TRAX ladder gets the mic's ballistics (and a 33 Hz beat)

Reported: the TRAX bar moves, but its sampling looks far slower than the mic meter.

Cause: the TRAX number was a raw instantaneous peak per metering block — a stutter sampled by the UI
timer, with no smoothing. The mic looks fluid because it is smoothed at audio-callback rate.

Fix: the player now smooths its measured level with the SAME curve the mic uses
(MeterScale.NextLevel: fast attack, gentle decay), and the dock's meter clock runs at ~30 Hz instead
of 20. Two ladders that move alike, because they are the same ballistics.

Guard: MeterScaleTests pins the attack/decay behaviour alongside peak-hold.

Helpers/MeterScale.cs

@@ -34,6 +34,15 @@ public static class MeterScale
          : dbfs >= CautionDb ? MeterBand.Caution
          : MeterBand.Nominal;
 
+    /// <summary>Ballistics for a level: reach a new peak quickly, fall back gently. Raw per-block
+    /// peaks sampled by a UI timer look like a stutter; this is what makes the mic feel fluid, and
+    /// TRAX gets the same curve so the two ladders move alike.</summary>
+    public static float NextLevel(float current, float incoming, float attack = 0.6f, float decay = 0.12f)
+    {
+        var alpha = incoming > current ? attack : decay;
+        return current + (incoming - current) * alpha;
+    }
+
     /// <summary>Peak hold: jumps up instantly to a new maximum and falls back at
     /// <paramref name="decayPerSecond"/> — a moment-to-moment bar hides clipping, which is the one
     /// audio fault that cannot be fixed afterwards.</summary>