C2(deploy-infra-alerting): impl fix TextfileStale noDataState to OK

Same pattern as PodNotReady: when no textfiles are stale, the query
returns no data. noDataState=Alerting incorrectly treats this as a
problem. Changed to OK.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

argocd/manifests/grafana/alerting.yaml

@@ -93,7 +93,7 @@ groups:
         title: TextfileStale
         condition: C
         for: 15m
-        noDataState: Alerting
+        noDataState: OK
         execErrState: Alerting
         annotations:
           summary: >-