feat(ui): show YouTube-confirmed live state in top bar

Normal ON-AIR stays red until YouTube reports lifeCycleStatus=live, then turns green; TEST stays gold and stop restores the idle color.

Status-color reference: https://www.carbondesignsystem.com/building-blocks/core/patterns/status-indicators

ytLive.Tests/OnAirSignTests.cs

@@ -1,22 +1,21 @@
 using System;
 using System.ComponentModel;
 using Xunit;
+using ytLive.Helpers;
 using ytLive.Models;
 using ytLive.ViewModels;
 
 namespace ytLive.Tests;
 
 /// <summary>
-/// The ON-AIR sign (right of REC in the top bar): gray offline, red when
-/// streaming public, green when streaming private. Driven through the real
-/// MainViewModel so StreamStatus/StreamVisibility notification wiring is
-/// exercised, not just the computed property.
+/// The ON-AIR sign and menu-bar color follow the real MainViewModel state,
+/// including the YouTube lifecycle confirmation before the bar turns green.
 /// </summary>
 [Collection("RealApp")]
 public sealed class OnAirSignTests
 {
     [Fact]
-    public void OnAirBrush_Follows_Offline_Public_And_Private()
+    public void OnAirBrush_And_TopBarBackground_Follow_YouTube_Live_State()
     {
         _app.Run(Run);
     }
@@ -38,6 +37,7 @@ public sealed class OnAirSignTests
 
             Assert.Equal(StreamStatus.Offline, vm.StreamStatus);
             Assert.Equal("#5b6478", vm.OnAirBrush);
+            var idleBackground = vm.TopBarBackground;
 
             var raised = 0;
             vm.PropertyChanged += (_, e) => { if (e.PropertyName == nameof(MainViewModel.OnAirBrush)) raised++; };
@@ -47,11 +47,28 @@ public sealed class OnAirSignTests
 
             vm.StreamStatus = StreamStatus.Streaming;
             Assert.Equal("#ff5451", vm.OnAirBrush);
+            Assert.Equal(ThemeBrush.Hex("Brush.Primary"), vm.TopBarBackground);
+
+            vm.ApplyBroadcastLifecycleStatus("liveStarting");
+            Assert.Equal(ThemeBrush.Hex("Brush.Primary"), vm.TopBarBackground);
 
             vm.StreamVisibility = "Private";
             Assert.Equal("#22c55e", vm.OnAirBrush);
 
             Assert.Equal(3, raised);
+            vm.ApplyBroadcastLifecycleStatus("live");
+            Assert.Equal(ThemeBrush.Hex("Brush.Positive"), vm.TopBarBackground);
+
+            vm.StreamStatus = StreamStatus.Offline;
+            Assert.Equal(idleBackground, vm.TopBarBackground);
+
+            vm.IsTestStream = true;
+            vm.StreamStatus = StreamStatus.Streaming;
+            Assert.Equal(ThemeBrush.Hex("Brush.TestContainer"), vm.TopBarBackground);
+            vm.ApplyBroadcastLifecycleStatus("live");
+            Assert.Equal(ThemeBrush.Hex("Brush.TestContainer"), vm.TopBarBackground);
+            vm.StreamStatus = StreamStatus.Offline;
+            Assert.Equal(idleBackground, vm.TopBarBackground);
         }
         finally
         {