design: the code-set state colours now agree with the standard

Last inconsistency from the sweep: several VM-side state colours are still literals, and after
the palette moved they disagreed with everything around them — the top bar's LIVE state would
have painted the retired pink-red while the tile beside it used the standard red.

Values aligned (tokenisation of these sites is its own unit — they are strings bound to
Background/Foreground, so the fix is a VM->Brush refactor, not a find/replace):
- live / on-air / recorder dot: #e94560 -> #ff5451 (the standard red)
- error banner: #8f1f1f -> #93000a (error-container)
- audio meter bands follow the doc's stated thresholds: nominal cyan #38bdf8, caution amber
  #ffb95f, peak #ff5451 — they were green/yellow/red, which contradicted DESIGN.md's own table

GameMeterHonestyTests pinned the old band colours; its intent (the meter scales by volume) is
unchanged, so the two colour expectations now name the new bands.

ViewModels/MainViewModel.Audio.cs

@@ -68,9 +68,9 @@ public partial class MainViewModel
 
     public string MeterBrush => MeterLevel switch
     {
-        < 0.6 => "#22c55e",
-        < 0.8 => "#eab308",
-        _ => "#ef4444",
+        < 0.6 => "#38bdf8",
+        < 0.8 => "#ffb95f",
+        _ => "#ff5451",
     };
 
     /// <summary>Previewes the volume position while the slider is dragged; the
@@ -283,9 +283,9 @@ public partial class MainViewModel
 
     public string GameMeterBrush => GameMeterLevel switch
     {
-        < 0.6 => "#22c55e",
-        < 0.8 => "#eab308",
-        _ => "#ef4444",
+        < 0.6 => "#38bdf8",
+        < 0.8 => "#ffb95f",
+        _ => "#ff5451",
     };
 
     public void SetGameVolumeAdjusting(bool adjusting)