PERF(observability): reduce replicas, add priority

- Reduce Prometheus replicas from 2 to 1
- Reduce Grafana replicas from 2 to 1
- Reduce Blackbox-exporter replicas from 2 to 1
- Move Loki, Thanos, Tempo to workers (remove tolerations)
- Add medium-priority to Prometheus, Loki, Thanos, Tempo

thanos/helm-values.yaml

@@ -29,13 +29,8 @@ query:
   enabled: true
   replicaCount: 1
 
-  # Run on master node for stability
-  tolerations:
-    - key: node-role.kubernetes.io/control-plane
-      operator: Exists
-      effect: NoSchedule
-  nodeSelector:
-    node-role.kubernetes.io/control-plane: "true"
+  # Medium priority for observability
+  priorityClassName: medium-priority
 
   # Deduplicate metrics from multiple Prometheus replicas
   dnsDiscovery: