Fix Frigate preview config and services-check NoData detection

preview.quality was at the top level (invalid); moved under record
with a valid preset (very_low). Also fix services-check to catch
Grafana "Alerting (NoData)" state which was silently passing.

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

argocd/manifests/frigate/frigate-config.yml

@@ -67,11 +67,10 @@ model:
   path: /media/frigate/models/yolov9-c-640.onnx
   labelmap_path: /labelmap/coco-80.txt
 
-preview:
-  quality: 8
-
 record:
   enabled: true
+  preview:
+    quality: very_low
   continuous:
     days: 30
   motion: