feat(ui): the capture context menu is always available (Ctrl+right-click); wordmark "ty" is YouTube red

1. The preview's right-click handler swallowed every right-click for the zoom box, so the
   element/backdrop context menu could not open at all. Sources and capture windows must be
   changeable AT ANY TIME — a creator swaps a window mid-stream without entering edit mode.
   Ctrl + right-click now bypasses the zoom path and lets WPF open the menu under the cursor;
   plain right-click keeps the zoom box. No menu markup changed.

2. The wordmark's "ty" is YouTube red (#ff0000), permanently. The token sweep had recoloured it
   to the interactive blue because it was a bare literal; DESIGN.md now records "never re-colour
   the wordmark" beside the token, and UiShellTests pins it.

Guard: UiShellTests gains the wordmark rule and the Ctrl+right-click chord.

ytLive.Tests/UiShellTests.cs

@@ -59,6 +59,19 @@ public class UiShellTests
         Assert.DoesNotContain("MaxHeight", listLine);
     }
 
+    [Fact]
+    public void The_wordmark_ty_stays_youtube_red_and_ctrl_opens_the_context_menu()
+    {
+        var topBar = SourceAssert.Text("Controls", "TopBar.xaml");
+        Assert.Contains("<Run Text=\"ty\" Foreground=\"{StaticResource Brush.Youtube}\"/>", topBar);
+
+        // Plain right-click is the zoom box; the context menu moved to Ctrl+right-click so a
+        // creator can change capture sources mid-stream.
+        var preview = SourceAssert.Text("Controls", "PreviewPane.xaml.cs");
+        Assert.Contains("ModifierKeys.Control", preview);
+        Assert.Contains("return;", preview);
+    }
+
     private static int Count(string haystack, string needle)
     {
         var hits = 0;