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.

Controls/PreviewPane.xaml

@@ -878,7 +878,7 @@
                             </Border>
                             <!-- The stacked white tabs -->
                             <StackPanel Orientation="Vertical" HorizontalAlignment="Right" VerticalAlignment="Stretch">
-                                <Border Width="30" VerticalAlignment="Center" Background="{StaticResource Brush.Attention}"
+                                <Border Width="30" VerticalAlignment="Center" Background="{StaticResource Brush.Youtube}"
                                         CornerRadius="4,0,0,4" Padding="0,10" Cursor="Hand" Margin="0,4,0,0"
                                         ToolTip="Broadcast text fields">
                                     <Border.InputBindings>
@@ -899,7 +899,7 @@
                                     </TextBlock>
                                 </StackPanel>
                                 </Border>
-                                <Border Width="30" VerticalAlignment="Center" Background="{StaticResource Brush.Attention}"
+                                <Border Width="30" VerticalAlignment="Center" Background="{StaticResource Brush.Youtube}"
                                         CornerRadius="4,0,0,4" Padding="0,10" Cursor="Hand" Margin="0,4,0,0"
                                         ToolTip="YouTube Partner Program progress">
                                     <Border.InputBindings>