Preserve failure nf status set by recordFinalError in buildZuulHttpResponse (#2131)

When origin.recordFinalError() sets a specific failure StatusCategory
(e.g. from an origin subclass override), the subsequent unconditional
setStatusCategory call was overwriting it with the generic status
derived from the response code.

This PR switches to use storeStatusCategoryIfNotAlreadyFailure so that a
failure status set by recordFinalError is not overwritten.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: lindseyreynolds

zuul-core/src/main/java/com/netflix/zuul/filters/endpoint/ProxyEndpoint.java

@@ -910,7 +910,7 @@ private HttpResponseMessage buildZuulHttpResponse(
         // Collect some info about the received response.
         origin.recordFinalResponse(zuulResponse);
         origin.recordFinalError(zuulRequest, ex);
-        StatusCategoryUtils.setStatusCategory(zuulCtx, statusCategory);
+        StatusCategoryUtils.storeStatusCategoryIfNotAlreadyFailure(zuulCtx, statusCategory);
         zuulCtx.setError(ex);
         zuulCtx.put("origin_http_status", Integer.toString(respStatus));