fix(monitoring): correct Loki Helm repo URL and set SingleBinary mode

- Fix repo URL: grafana-community.github.io → grafana.github.io
- Explicitly set deploymentMode: SingleBinary with replicas: 1
  for ARM64 single-node environment
- Remove loki.enabled (not a valid v6.x chart value)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: soohyunme

infrastructure/base/monitoring/loki/kustomization.yaml

@@ -5,7 +5,7 @@ namespace: monitoring
 
 helmCharts:
   - name: loki
-    repo: https://grafana-community.github.io/helm-charts
+    repo: https://grafana.github.io/helm-charts
     version: 6.55.0
     releaseName: loki
     namespace: monitoring

infrastructure/base/monitoring/loki/values.yaml

@@ -1,6 +1,10 @@
 # Loki k8s stack for single-node A1 (ARM64)
+deploymentMode: SingleBinary
+
+singleBinary:
+  replicas: 1
+
 loki:
-  enabled: true
   auth_enabled: false
 
   ingester: