refactor(api): throw on unmapped health status instead of silent NotApplicable fallthrough (#108)

Review finding: NotApplicable is filtered by the handler before mapping,
so a silent ->"info" arm would only mask a missing filter if the mapper
is ever reused unfiltered.

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

ErsatzTV.Application/Health/Mapper.cs

@@ -19,7 +19,6 @@ internal static class Mapper
             HealthCheckStatus.Fail => "fail",
             HealthCheckStatus.Warning => "warn",
             HealthCheckStatus.Info => "info",
-            HealthCheckStatus.NotApplicable => "info",
-            _ => throw new ArgumentOutOfRangeException(nameof(status))
+            _ => throw new ArgumentOutOfRangeException(nameof(status), status, null)
         };
 }