fix: guard null scene name in scene-JS Sentry fingerprint and drop review-referencing test comment

SceneShortInfo.Name is declared non-nullable but a default(SceneShortInfo)
(no sceneShortInfo passed to ReportData) yields Name == null, since C#
does not enforce non-null defaults on struct fields. AddSceneJsFingerprint
forwarded that null straight into Scope.SetFingerprint's array instead of
handling the missing-scene case, and the accompanying test locked the null
passthrough in as intended behavior rather than exercising a real fallback.
Guard with a named UNKNOWN_SCENE_NAME constant so a missing scene never
ships a null fingerprint segment, and update the test to assert the
fallback value.

Also removes an AI-narration comment in SentryReportHandlerShould.cs that
referenced this diff's own review document by section number instead of
describing the test's behavior, replacing it with a plain rationale for
why the scene name is null in that scenario.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018c638dR1vPysCMbYt2qQg5

Author: eordano

Explorer/Assets/DCL/PerformanceAndDiagnostics/Diagnostics/ReportsHandling/Sentry/SentryReportHandler.cs

@@ -16,6 +16,7 @@ public class SentryReportHandler : ReportHandlerBase
         public delegate void ConfigureScope(Scope scope);
 
         private static readonly TimeSpan SESSION_FLUSH_TIMEOUT = TimeSpan.FromSeconds(2);
+        private const string UNKNOWN_SCENE_NAME = "unknown-scene";
 
         private readonly List<ConfigureScope> scopeConfigurators = new (10);
 
@@ -184,7 +185,7 @@ internal static void AddSceneJsFingerprint(Scope scope, in ReportData data, stri
             if (string.IsNullOrEmpty(exceptionMessage))
                 return;
 
-            scope.SetFingerprint(new[] { "scene-js", data.SceneShortInfo.Name, FirstLine(exceptionMessage) });
+            scope.SetFingerprint(new[] { "scene-js", data.SceneShortInfo.Name ?? UNKNOWN_SCENE_NAME, FirstLine(exceptionMessage) });
         }
 
         private static string FirstLine(string message)

Explorer/Assets/DCL/PerformanceAndDiagnostics/Diagnostics/ReportsHandling/Tests/SentryReportHandlerShould.cs

@@ -48,17 +48,15 @@ public void NotSetFingerprintForNonJavaScriptCategory()
         }
 
         [Test]
-        public void SetFingerprintWithNullSceneNameWhenSceneShortInfoIsMissing()
+        public void SetFingerprintWithFallbackSceneNameWhenSceneShortInfoIsMissing()
         {
             // No sceneShortInfo supplied -> default(SceneShortInfo), Name == null.
-            // The patch does not special-case a missing scene: the null flows straight
-            // into the fingerprint array (documented residual risk in review.md #4).
             Scope scope = NewScope();
             var reportData = new ReportData(ReportCategory.JAVASCRIPT);
 
             SentryReportHandler.AddSceneJsFingerprint(scope, reportData, "Error: boom");
 
-            CollectionAssert.AreEqual(new[] { "scene-js", null, "Error: boom" }, scope.Fingerprint);
+            CollectionAssert.AreEqual(new[] { "scene-js", "unknown-scene", "Error: boom" }, scope.Fingerprint);
         }
     }
 }