Deploy sales/dev dataplane (Layer 2), mirroring catalog/customers/payments

Real Konnect Control Plane 84a3dd19-7daf-47e6-84ea-9ad5966b91a6, PAT
in Vault (kong-v2/sales/dev/konnect-pat). Replaces the TODO stubs
with the proven gateway-kustomization.yaml + externalsecret.yaml +
policies-kustomization.yaml pattern. JWT_AUDIENCE_WHITELIST includes
mcp-sales from the start since Layer 3 (REST + MCP) was built the
same session — see STATUS.md section 22.

dev/api-gateway/gateway-kustomization.yaml

@@ -0,0 +1,21 @@
+apiVersion: kustomize.toolkit.fluxcd.io/v1
+kind: Kustomization
+metadata:
+  name: sales-dev-api-gateway
+  namespace: flux-system
+spec:
+  interval: 10m
+  sourceRef:
+    kind: GitRepository
+    name: k8s-platform
+  path: ./dataplane-template
+  prune: true
+  postBuild:
+    substitute:
+      NAME: sales-dev
+      NAMESPACE: sales
+      CONTROL_PLANE_ID: "84a3dd19-7daf-47e6-84ea-9ad5966b91a6"
+      HOSTNAME: sales-dev.sttlab.local
+    substituteFrom:
+      - kind: ConfigMap
+        name: dataplane-template-defaults