Declare the label fixture's key on its base member

The registry requires an override to repeat or omit the base declaration's [Key].

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/GameCult.Caching.Tests/CultInspectorModelTests.cs

@@ -361,7 +361,7 @@ namespace GameCult.Caching.Tests
 
         public abstract class InspectLabeledBase
         {
-            [CultInspectorLabel("Base Label")]
+            [Key(1)] [CultInspectorLabel("Base Label")]
             public abstract string Tag { get; set; }
         }