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.

Themes/Controls.xaml

@@ -654,6 +654,31 @@
         <Setter Property="Margin" Value="8,0,0,0"/>
     </Style>
 
+    <!-- REC / ON-AIR segment pills: an armed session control reads red, because red is what
+         "live or recording" means (DESIGN.md). Kept separate from SegmentToggle so the Rect|Circle
+         choice in the properties panel stays the interactive blue. -->
+    <Style x:Key="RecordPillToggle" TargetType="ToggleButton" BasedOn="{StaticResource SegmentToggle}">
+        <!-- SegmentToggle's template hard-codes a Transparent face and paints the checked state
+             itself, so an armed pill needs its own template that honours Background. -->
+        <Setter Property="Background" Value="Transparent"/>
+        <Setter Property="Template">
+            <Setter.Value>
+                <ControlTemplate TargetType="ToggleButton">
+                    <Border x:Name="Seg" Background="{TemplateBinding Background}" CornerRadius="3"
+                            Padding="{TemplateBinding Padding}">
+                        <ContentPresenter HorizontalAlignment="Center" VerticalAlignment="Center"/>
+                    </Border>
+                </ControlTemplate>
+            </Setter.Value>
+        </Setter>
+        <Style.Triggers>
+            <Trigger Property="IsChecked" Value="True">
+                <Setter Property="Background" Value="{StaticResource Brush.Primary}"/>
+                <Setter Property="Foreground" Value="{StaticResource Brush.OnError}"/>
+            </Trigger>
+        </Style.Triggers>
+    </Style>
+
     <!-- Sliding pill toggle: OFF = neutral, ON = blue. Red is reserved for live/record
          (DESIGN.md), so a settings toggle can never use it. -->
     <Style x:Key="PillToggle" TargetType="ToggleButton">