Use sorted username dropdown for character owner editing

RpgRoller.Tests/Services/ServiceAuthTests.cs

@@ -56,4 +56,22 @@ public sealed class ServiceAuthTests
         Assert.True(login.Succeeded);
         Assert.Equal(2, hasher.HashCalls);
     }
-}
+
+    [Fact]
+    public void GetUsernames_RequiresAuthAndReturnsSortedUsernames()
+    {
+        using var harness = ServiceTestSupport.CreateHarness();
+        var service = harness.Service;
+
+        service.Register("zoe", "Password123", "Zoe");
+        service.Register("amy", "Password123", "Amy");
+        service.Register("bob", "Password123", "Bob");
+
+        var unauthorized = service.GetUsernames(string.Empty);
+        Assert.False(unauthorized.Succeeded);
+
+        var session = ServiceTestSupport.GetValue(service.Login("bob", "Password123")).SessionToken;
+        var usernames = ServiceTestSupport.GetValue(service.GetUsernames(session));
+        Assert.Equal(["amy", "bob", "zoe"], usernames);
+    }
+}