feat(scoreboard): dev mode can configure the board without signing in

Creator (2026-10-30): in dev mode the "Show the scoreboard" option must always be available.

The block's gate becomes CanUseScoreboard = IsConnected || IsDevelopmentBuild. Signed-out Release
still shows the inert block with its "sign in" line; a DEBUG build is fully usable, so the strip can
be toggled and previewed before there is an account. IsConnected raises it, so signing in flips it
live.

Guard: ScoreboardPropertiesTests now asserts the CanUseScoreboard gate (enabled AND hint), and the
VM surface list includes it.

Controls/LeftPanel.xaml

@@ -456,10 +456,10 @@
                                  inert until there is an account; signing in re-enables them through
                                  the ordinary IsConnected notification. -->
                             <StackPanel Visibility="{Binding SelectedElement.IsScoreboard, Converter={StaticResource BoolToVis}}"
-                                        IsEnabled="{Binding IsConnected}" Margin="0,0,0,8">
+                                        IsEnabled="{Binding CanUseScoreboard}" Margin="0,0,0,8">
                                 <TextBlock Text="Sign in to YouTube to use the scoreboard."
                                            Foreground="{StaticResource Brush.OnSurfaceVariant}" FontSize="11" Margin="0,0,0,4"
-                                           Visibility="{Binding IsConnected, Converter={StaticResource InverseBoolToVis}}"/>
+                                           Visibility="{Binding CanUseScoreboard, Converter={StaticResource InverseBoolToVis}}"/>
                                 <!-- DEBUG builds only: prove the strip in the preview before a real
                                      stream. Absent from Release, not merely hidden by a flag. -->
                                 <CheckBox Style="{StaticResource YtCheckBox}" Margin="0,0,0,4"

ViewModels/MainViewModel.Account.cs

@@ -17,6 +17,7 @@ public partial class MainViewModel
         {
             if (SetProperty(ref _isConnected, value))
             {
+                OnPropertyChanged(nameof(CanUseScoreboard));
                 // ON-AIR requires a sign-in; dropping the session turns the pill
                 // off so the state can never offer a stream without an account.
                 if (!value) OnAirPillOn = false;

ViewModels/MainViewModel.Scoreboard.cs

@@ -51,6 +51,11 @@ public partial class MainViewModel
     private const bool DevelopmentBuild = false;
 #endif
 
+    /// <summary>Can the scoreboard be configured at all? Signed-in creators yes; in a DEBUG build
+    /// always, so the strip can be previewed and judged before there is an account (creator,
+    /// 2026-10-30).</summary>
+    public bool CanUseScoreboard => IsConnected || IsDevelopmentBuild;
+
     /// <summary>True in a DEBUG build. Used only to expose development-only controls, never to
     /// change behaviour — the shipped binary differs by their absence, not by a code path.</summary>
     public bool IsDevelopmentBuild => DevelopmentBuild;

ytLive.Tests/ScoreboardPropertiesTests.cs

@@ -17,13 +17,13 @@ public class ScoreboardPropertiesTests
         // Gated on the selected layer being a scoreboard.
         Assert.Contains("SelectedElement.IsScoreboard", panel);
 
-        // Signed out: the whole block is inert (the board is fed by the signed-in channel), with a
-        // one-line explanation. Signing in re-enables it through the ordinary IsConnected raise.
+        // Signed out: the block is inert with a one-line explanation — EXCEPT in a DEBUG build, where
+        // CanUseScoreboard is true so the strip can be previewed without an account.
         var block = panel[panel.IndexOf("Scoreboard config", System.StringComparison.Ordinal)..];
         block = block[..block.IndexOf("<!-- Countdown config -->", System.StringComparison.Ordinal)];
-        Assert.Contains("IsEnabled=\"{Binding IsConnected}\"", block);
+        Assert.Contains("IsEnabled=\"{Binding CanUseScoreboard}\"", block);
         Assert.Contains("Sign in to YouTube to use the scoreboard.", block);
-        Assert.Contains("InverseBoolToVis", block);
+        Assert.Contains("CanUseScoreboard, Converter={StaticResource InverseBoolToVis}", block);
 
         // The master switch sits in the same panel: off hides the strip and stops the polling.
         Assert.Contains("ScoreboardEnabled", panel);
@@ -57,7 +57,7 @@ public class ScoreboardPropertiesTests
                  {
                      "ScoreboardTextColor", "ScoreboardBackgroundColor", "ScoreboardBackgroundOpacity",
                      "ScoreboardFontSize", "ScoreboardColorOptions", "ScoreboardShowSubscribers",
-                     "ScoreboardEnabled",
+                     "ScoreboardEnabled", "CanUseScoreboard",
                  })
             Assert.NotNull(type.GetProperty(name));
     }