Add VictoriaMetrics observability stack + sync catalog for monitoring test

- VM stack 10 charts: victoria-metrics-cluster/auth, victoria-logs-cluster,
  victoria-metrics-agent/alert, opentelemetry-collector, kube-state-metrics,
  prometheus-node-exporter, alertmanager, perses (JWT/OIDC, Infisical-ready)
- ArgoCD ApplicationSet (syncWave) + per-chart dip-values overlays
- doc/victoria-metrics-architecture.md, define-chart-resources updates
- includes pending working-tree changes (mlflow, kubeflow, apisix, CLAUDE.md)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

manifests/helm/alertmanager/1.37.0/custom-values.yaml

@@ -0,0 +1,51 @@
+# =============================================================================
+# Alertmanager — PaaSup 커스텀 오버라이드 (알림 라우팅·중복제거·Discord 발송)
+# 차트: prometheus-community/alertmanager
+# 수신: vmalert가 notifier로 알림 전송 (alertmanager:9093)
+#
+# Discord Webhook URL 주입 (값 파일에 평문 기입 금지):
+#   kubectl create secret generic alertmanager-discord -n monitoring \
+#     --from-literal=webhook-url="https://discord.com/api/webhooks/..."
+#   → extraSecretMounts로 마운트 후 discord_configs.webhook_url_file 로 참조
+# =============================================================================
+
+extraSecretMounts:
+  - name: alertmanager-discord
+    mountPath: /etc/alertmanager/secrets
+    subPath: ""
+    secretName: alertmanager-discord
+    readOnly: true
+
+config:
+  global:
+    resolve_timeout: 5m
+
+  route:
+    group_by: [alertname, severity]
+    group_wait: 30s
+    group_interval: 5m
+    repeat_interval: 4h
+    receiver: discord
+
+  receivers:
+    - name: discord
+      discord_configs:
+        - webhook_url_file: /etc/alertmanager/secrets/webhook-url
+          title: '[{{ .Status | toUpper }}] {{ .GroupLabels.alertname }}'
+          message: |
+            {{ range .Alerts -}}
+            **{{ .Labels.severity | toUpper }}** {{ .Annotations.summary }}
+            {{- if .Annotations.description }}
+            {{ .Annotations.description }}
+            {{- end }}
+            {{ end }}
+
+  inhibit_rules:
+    - source_match:
+        severity: critical
+      target_match:
+        severity: warning
+      equal: [alertname, node]
+
+persistence:
+  enabled: false