fix(dock): meters beat on their own 20 Hz clock, and TRAX silence is diagnosed

Reported: TRAX plays audibly but no ladder registers anywhere.

Two distinct faults, one of them mine:
1. The meter readouts were refreshed only from the MIC's level callback. With a silent or absent
   mic there is no tick, so a playing TRAX never updated its ladder — the level was measured, the
   UI simply never asked for it. Meters now have a 20 Hz DispatcherTimer of their own.
2. If the player's own meter still reads 0 while playing, the samples are not reaching the device
   (or metering is not attached). That now writes ONE line to startup.log after 2s — so the next
   report says which side is broken instead of another round of guessing.

Note: TRAX rides the desktop loopback, so once the mix captures it the GAME ladder should move too;
if it does not, the loopback endpoint and the music's output device differ.

ViewModels/MainViewModel.cs

@@ -178,6 +178,13 @@ public partial class MainViewModel : ViewModelBase
         _gameVolumeFlashTimer.Tick += (_, _) => EndGameVolumeFlash();
 
         _saveDebounce = new DispatcherTimer { Interval = TimeSpan.FromMilliseconds(1500) };
+
+        // Dock meters beat on their own 20 Hz clock instead of riding the mic's level callback.
+        // Coupling them to capture was a bug: with a silent or absent mic the ladder never
+        // refreshed, so a playing TRAX showed nothing (creator, 2026-10-30).
+        _meterTimer = new DispatcherTimer { Interval = TimeSpan.FromMilliseconds(50) };
+        _meterTimer.Tick += (_, _) => TickMeters();
+        _meterTimer.Start();
         _saveDebounce.Tick += (_, _) => SaveLayoutNow();
 
         _brandFlash = new BrandFlashPresenter();