Harden prod: security, autoscaling, observability, BuildKit CI

Security:
- Drop ALL capabilities, enforce non-root, RuntimeDefault seccomp on
  neuron-mcp, neuron-rest, neuron-marketing pods
- Add startup probes (150s window for JVM) so liveness doesn't fire early
- Replace docker-sock hostPath with BuildKit rootless TCP endpoint
  (moby/buildkit:v0.19.0-rootless) — removes node root access from CI
- Document full ESO AppRole migration path in cluster-secret-store.yaml

Autoscaling & availability:
- HPAs on mcp (1–6), rest (1–4), marketing (2–8) at 65–70% CPU
- PodDisruptionBudgets (minAvailable: 1) on all three services
- NetworkPolicy: default-deny-all in neuron-prod, explicit allow rules
  for Traefik ingress, intra-namespace, and egress to DNS/platform/vault

Observability:
- ServiceMonitors for mcp, rest, marketing (cross-namespace enabled in
  kube-prometheus-stack with serviceMonitorSelectorNilUsesHelmValues:false)
- PrometheusRules: high error rate, high latency, crash loops, replica
  shortage, Postgres down/connections, backup failure, backup staleness

Chart version pinning:
- kube-prometheus-stack, loki, tempo, redis, alloy, postgres — all pinned
  to major-version ranges to block silent breaking upgrades

Backup hardening:
- restic:latest → restic:0.17.3 (deterministic image)
- Weekly backup-verify CronJob: restores latest snapshot and validates
  SQL dump structure (≥5 CREATE TABLE, pg_dump header check)

ArgoCD:
- neuron-prod AppProject: scopes deploys to neuron-prod + platform ns,
  blacklists ClusterRole/ClusterRoleBinding/Namespace creation,
  automated sync window 2–6am UTC, manual always allowed

servers/legion/k8s/monitoring/servicemonitor.yaml

@@ -0,0 +1,64 @@
+---
+# ServiceMonitors for neuron-prod — scraped by kube-prometheus-stack Prometheus
+# Requires: kube-prometheus-stack prometheusSpec.serviceMonitorSelectorNilUsesHelmValues=false
+# OR a serviceMonitorNamespaceSelector that includes neuron-prod.
+# We set this in the Prometheus stack values (see apps/kube-prometheus-stack.yaml).
+apiVersion: monitoring.coreos.com/v1
+kind: ServiceMonitor
+metadata:
+  name: neuron-mcp
+  namespace: monitoring
+  labels:
+    release: kube-prometheus-stack
+spec:
+  namespaceSelector:
+    matchNames:
+      - neuron-prod
+  selector:
+    matchLabels:
+      app: neuron-mcp
+  endpoints:
+    - port: http
+      path: /actuator/prometheus
+      interval: 30s
+      scrapeTimeout: 10s
+---
+apiVersion: monitoring.coreos.com/v1
+kind: ServiceMonitor
+metadata:
+  name: neuron-rest
+  namespace: monitoring
+  labels:
+    release: kube-prometheus-stack
+spec:
+  namespaceSelector:
+    matchNames:
+      - neuron-prod
+  selector:
+    matchLabels:
+      app: neuron-rest
+  endpoints:
+    - port: http
+      path: /actuator/prometheus
+      interval: 30s
+      scrapeTimeout: 10s
+---
+apiVersion: monitoring.coreos.com/v1
+kind: ServiceMonitor
+metadata:
+  name: neuron-marketing
+  namespace: monitoring
+  labels:
+    release: kube-prometheus-stack
+spec:
+  namespaceSelector:
+    matchNames:
+      - neuron-prod
+  selector:
+    matchLabels:
+      app: neuron-marketing
+  endpoints:
+    - port: http
+      path: /api/metrics
+      interval: 60s
+      scrapeTimeout: 15s