Wire marketplace Postgres datasource for neuron-mcp

Add MARKETPLACE_DB_URL/USER to ConfigMap and MARKETPLACE_DB_PASSWORD
ExternalSecret (sourced from secret/legion-db in Vault). Remove the
SQLite subPath volume mount and fix-data-ownership initContainer from
the blue deployment — marketplace storage is now in Postgres.

servers/legion/k8s/neuron-technologies/prod/mcp-deployment.yaml

@@ -22,7 +22,7 @@ spec:
         slot: blue
         env: prod
       annotations:
-        config-hash: "marketplace-db-subpath-v3"
+        config-hash: "marketplace-postgres-v1"
     spec:
       terminationGracePeriodSeconds: 30
       securityContext:
@@ -30,16 +30,6 @@ spec:
         runAsUser: 1000
         seccompProfile:
           type: RuntimeDefault
-      initContainers:
-        - name: fix-data-ownership
-          image: busybox:1.36
-          command: ["sh", "-c", "touch /data/neuron-marketplace.db && chown -R 1000:1000 /data"]
-          securityContext:
-            runAsUser: 0
-            runAsNonRoot: false
-          volumeMounts:
-            - name: data
-              mountPath: /data
       containers:
         - name: neuron-mcp
           image: registry.neuralplatform.ai/neuron-technologies/neuron-mcp:v0.15.3
@@ -67,9 +57,6 @@ spec:
           volumeMounts:
             - name: data
               mountPath: /data
-            - name: data
-              mountPath: /app/neuron-marketplace.db
-              subPath: neuron-marketplace.db
           resources:
             requests:
               cpu: 250m