deploy engram-server to neuron-prod: dharma storage backend

- Add engram-server Deployment, Service, PVC to neuron-prod
- engram-server is the graph memory substrate for DHARMA registry
- Add allow-engram-ingress NetworkPolicy (ingress from neuron-prod)
- ENGRAM_URL in Vault updated to http://engram-server.neuron-prod.svc.cluster.local:8742
- Image: registry.neuralplatform.ai/neuron-technologies/engram-server:latest
  compiled from foundation/engram dist/engram.c + el_runtime

servers/legion/k8s/neuron-technologies/prod/network-policy.yaml

@@ -99,6 +99,24 @@ spec:
             matchLabels:
               kubernetes.io/metadata.name: kube-system
 ---
+# ── engram-server: accept from dharma and neuron-prod namespace ──────────────
+apiVersion: networking.k8s.io/v1
+kind: NetworkPolicy
+metadata:
+  name: allow-engram-ingress
+  namespace: neuron-prod
+spec:
+  podSelector:
+    matchLabels:
+      app: engram-server
+  policyTypes:
+    - Ingress
+  ingress:
+    - from:
+        - namespaceSelector:
+            matchLabels:
+              kubernetes.io/metadata.name: neuron-prod
+---
 # ── Egress: all prod pods may reach platform (postgres/redis), vault,
 #            monitoring (alloy OTLP), kube-dns, and the internet (external APIs) ─
 apiVersion: networking.k8s.io/v1