fix(viewer): fresh signups start with empty DisplayName

Verified against Wizard.Title/UserNameInput.cs:30 in the 2026-05-23
decompile:

    IsFinished = !string.IsNullOrEmpty(PlayerStaticData.UserName);

Any non-empty seeded value — including the prior " - " placeholder
this method was passing — sets IsFinished=true on the first frame and
silently skips both the input dialog and the /tutorial/update_action #1
+ /account/update_name calls that travel with it. The in-source comment
described the opposite behavior; empty string is what actually triggers
the dialog.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.UnitTests/Repositories/ViewerRepositoryTutorialDefaultTests.cs

@@ -25,4 +25,23 @@ public class ViewerRepositoryTutorialDefaultTests
             "client. Tests that want a pre-completed tutorial should use SeedViewerAsync " +
             "(which defaults to 100).");
     }
+
+    [Test]
+    public async Task RegisterAnonymousViewer_starts_with_empty_display_name()
+    {
+        // The client's Wizard.Title/UserNameInput.Start does:
+        //   IsFinished = !string.IsNullOrEmpty(PlayerStaticData.UserName);
+        // Any non-empty seeded value (including the prior " - " placeholder) makes the
+        // name-input dialog skip itself, and the /tutorial/update_action #1 +
+        // /account/update_name calls never fire. Empty is what triggers the dialog.
+        using var factory = new SVSimTestFactory();
+        using var scope = factory.Services.CreateScope();
+        var repo = scope.ServiceProvider.GetRequiredService<IViewerRepository>();
+
+        var viewer = await repo.RegisterAnonymousViewer(System.Guid.NewGuid());
+
+        Assert.That(viewer.DisplayName, Is.Empty,
+            "Anonymous signups MUST start with empty DisplayName so the client's " +
+            "UserNameInput.Start IsNullOrEmpty short-circuit fails and the dialog runs.");
+    }
 }