feat(ui): the creator's six corrections

1. Stream Info + YPP rails are YouTube surfaces → new `youtube` token #ff0000. It is documented
   as brand-only: live state stays `primary`, so the two reds never mean the same thing.
2. EDIT toggle: the checked trigger set the SAME colour as the resting face, so clicking it
   changed nothing visible. Resting is now the neutral surface with muted text; armed is blue with
   dark text, and the label follows the fill.
3. Active scene outline is orange again (`attention`) — it marks the scene you work on, not a
   selection; blue made it read as "selected". Live stays red.
4. Scene names wear the same pill as the hotkey chips (black, 10px radius, 8×2 padding), so both
   labels stay readable over any thumbnail.
5. REC / ON-AIR pills and the running stop button read red while armed/live — including test
   mode, where the top bar is gold. New `RecordPillToggle` style (its own template, because
   SegmentToggle hard-codes a transparent face); the stop button's grey `#333` literal is gone.
6. The properties list had `MaxHeight="420"` inside an Auto row, so it scrolled while the window
   had space left. The row is `*` now and the cap is gone.

Guard: UiShellTests pins all six to the markup and names the one that regresses.

ytLive.Tests/UiShellTests.cs

@@ -0,0 +1,63 @@
+using System.Linq;
+using Xunit;
+
+namespace ytLive.Tests;
+
+/// <summary>The creator's six corrections (2026-10-30) are visual rulings, so the only honest guard
+/// is one that pins the ruling to the markup: if a later edit quietly reverts one of them, this
+/// fails and names it.
+///
+/// <para>1. Stream Info + YPP rails are YouTube surfaces (YouTube red). 2. EDIT shows a real
+/// off/on difference. 3. The active scene outline is orange again. 4. Scene labels wear the same
+/// pill as the hotkey chips. 5. REC / ON-AIR and the running stop button read red. 6. The
+/// properties list no longer caps its height, so no scrollbar appears while space remains.</para></summary>
+public class UiShellTests
+{
+    [Fact]
+    public void The_creators_six_ui_corrections_are_in_the_markup()
+    {
+        var preview = SourceAssert.Text("Controls", "PreviewPane.xaml");
+        var topBar = SourceAssert.Text("Controls", "TopBar.xaml");
+        var strip = SourceAssert.Text("Controls", "SceneThumbnailStrip.xaml");
+        var leftPanel = SourceAssert.Text("Controls", "LeftPanel.xaml");
+        var theme = SourceAssert.Text("Themes", "Controls.xaml");
+        var tokens = SourceAssert.Text("Themes", "Tokens.xaml");
+
+        // 1. YouTube-branded rails.
+        Assert.Contains("Brush.Youtube", tokens);
+        Assert.Equal(2, Count(preview, "Background=\"{StaticResource Brush.Youtube}\""));
+
+        // 2. EDIT: resting face differs from the armed face, and the label follows it.
+        Assert.Contains("x:Name=\"EditBody\" Background=\"{StaticResource Brush.SurfaceContainerHigh}\"", topBar);
+        Assert.Contains("<Setter TargetName=\"EditBody\" Property=\"Background\" Value=\"{StaticResource Brush.Tertiary}\"/>", topBar);
+        Assert.Contains("<Setter Property=\"Foreground\" Value=\"{StaticResource Brush.OnTertiary}\"/>", topBar);
+
+        // 3. Active scene = orange; live stays red.
+        Assert.Contains("IsStaged}\" Value=\"True\">\n                                        <Setter Property=\"BorderBrush\" Value=\"{StaticResource Brush.Attention}\"/>", strip);
+
+        // 4. Scene name pill, same shape as the hotkey chip.
+        Assert.Contains("Padding=\"8,2\" CornerRadius=\"10\" Background=\"#000000\"", strip);
+        Assert.Contains("Text=\"{Binding Name, Mode=OneWay}\"", strip);
+
+        // 5. Armed session controls are red, and the running stop button is red — not a grey literal.
+        Assert.Contains("x:Key=\"RecordPillToggle\"", theme);
+        Assert.Contains("Brush.Primary", theme);
+        Assert.Contains("Style=\"{StaticResource RecordPillToggle}\"", topBar);
+        Assert.Contains("Background=\"{StaticResource Brush.Primary}\" Margin=\"14,0,0,0\"", topBar);
+        Assert.DoesNotContain("Background=\"#333\"", topBar);
+
+        // 6. No artificial height cap on the properties list: the list fills the row, so a
+        //    scrollbar appears only when the content genuinely exceeds the space.
+        var listLine = leftPanel.Split('\n').First(line => line.Contains("ElementsScrollViewer"));
+        Assert.DoesNotContain("MaxHeight", listLine);
+    }
+
+    private static int Count(string haystack, string needle)
+    {
+        var hits = 0;
+        for (var i = haystack.IndexOf(needle, System.StringComparison.Ordinal); i >= 0;
+             i = haystack.IndexOf(needle, i + needle.Length, System.StringComparison.Ordinal))
+            hits++;
+        return hits;
+    }
+}