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.

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;