feat(spark): add staging overlay, scale down prod

- spark-cluster/eu-central-1-staging: namespace nowchess-staging, ingress
  patched to spark-st.* / spark-history-st.* with TLS + cert-manager
- spark-analytics/eu-central-1-staging: namespace nowchess-staging, image
  pinned to 0.2.0, all CronJob + live-dashboard patches carried over
- eu-central-1/argo-apps: spark-cluster-staging + spark-analytics-staging
  ArgoCD apps pointing at new staging overlays
- spark-cluster/eu-central-1-prod: scale spark-master and spark-worker to 0

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

eu-central-1/argo-apps/spark-analytics/spark-analytics-staging.yaml

@@ -0,0 +1,18 @@
+apiVersion: argoproj.io/v1alpha1
+kind: Application
+metadata:
+  name: spark-analytics-staging
+  namespace: argocd
+spec:
+  project: default
+  destination:
+    namespace: nowchess-staging
+    server: https://kubernetes.default.svc
+  sources:
+    - repoURL: git@git.janis-eccarius.de:NowChess/Gitops.git
+      path: ./spark-analytics/eu-central-1-staging
+      targetRevision: main
+  syncPolicy:
+    automated:
+      prune: true
+      selfHeal: true

eu-central-1/argo-apps/spark-cluster/spark-cluster-staging.yaml

@@ -0,0 +1,18 @@
+apiVersion: argoproj.io/v1alpha1
+kind: Application
+metadata:
+  name: spark-cluster-staging
+  namespace: argocd
+spec:
+  project: default
+  destination:
+    namespace: nowchess-staging
+    server: https://kubernetes.default.svc
+  sources:
+    - repoURL: git@git.janis-eccarius.de:NowChess/Gitops.git
+      path: ./spark-cluster/eu-central-1-staging
+      targetRevision: main
+  syncPolicy:
+    automated:
+      prune: true
+      selfHeal: true