devops(observability): fix C4 diagram, security comment, and add Loki compactor block

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

infra/observability/loki/loki-config.yml

@@ -28,5 +28,13 @@ schema_config:
 limits_config:
   retention_period: 720h  # 30 days — low-volume family archive; revisit if log volume grows
 
+compactor:
+  working_directory: /loki/compactor
+  compaction_interval: 10m
+  retention_enabled: true
+  retention_delete_delay: 2h
+  retention_delete_worker_count: 150
+  delete_request_store: filesystem
+
 analytics:
   reporting_enabled: false  # no telemetry sent to Grafana Labs