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

Real Konnect Control Plane dc3b2a36-e2ad-4da1-a142-022d0ce6d94e, PAT
in Vault (kong-v2/payments/dev/konnect-pat). Replaces the TODO stubs
with the proven gateway-kustomization.yaml + externalsecret.yaml +
policies-kustomization.yaml pattern. IdP is the local Keycloak from
the start (platform default now, see STATUS.md 15/16), not the VPS.

Layer 3 (payments-api) not started — Gateway answers 404, nothing
routed yet.

dev/api-gateway/dataplane.yaml

@@ -1,5 +0,0 @@
-# TODO: DataPlane CRD for payments/dev/api-gateway
-apiVersion: gateway-operator.konghq.com/v1beta1
-kind: DataPlane
-metadata:
-  name: payments-dev

dev/api-gateway/externalsecret.yaml

@@ -0,0 +1,27 @@
+# Real PAT lives only in Vault (secrets/kong-v2/payments/dev/konnect-pat),
+# never in git, never manually kubectl-applied. refreshInterval controls how
+# often ESO re-checks Vault and re-syncs the K8s Secret if the value
+# changed there — rotation becomes "update Vault", nothing to touch in the
+# cluster.
+apiVersion: external-secrets.io/v1
+kind: ExternalSecret
+metadata:
+  name: payments-dev-konnect-auth
+  namespace: payments
+spec:
+  refreshInterval: 1h
+  secretStoreRef:
+    kind: ClusterSecretStore
+    name: vault-kong-v2
+  target:
+    name: payments-dev-konnect-auth
+    template:
+      metadata:
+        labels:
+          konghq.com/credential: konnect
+          konghq.com/secret: "true"
+  data:
+    - secretKey: token
+      remoteRef:
+        key: kong-v2/payments/dev/konnect-pat
+        property: token

dev/api-gateway/gateway-kustomization.yaml

@@ -0,0 +1,37 @@
+# sourceRef points at the GitRepository "k8s-platform" (created once,
+# flux-system) — any domain's Kustomization can reference this same
+# object, no monorepo: k8s-platform and dataplane-payments stay two
+# separate repos, `path` below is relative to the root of whichever repo
+# `sourceRef` names.
+apiVersion: kustomize.toolkit.fluxcd.io/v1
+kind: Kustomization
+metadata:
+  name: payments-dev-api-gateway
+  namespace: flux-system
+spec:
+  interval: 10m
+  sourceRef:
+    kind: GitRepository
+    name: k8s-platform
+  path: ./dataplane-template
+  prune: true
+  postBuild:
+    # Domain-specific non-sensitive values inline — no separate ConfigMap to
+    # forget to re-apply after an edit. Inline substitute always wins over
+    # substituteFrom regardless of order, so this still overrides
+    # dataplane-template-defaults where needed.
+    substitute:
+      NAME: payments-dev
+      NAMESPACE: payments
+      CONTROL_PLANE_ID: "dc3b2a36-e2ad-4da1-a142-022d0ce6d94e"
+      HOSTNAME: payments-dev.sttlab.local
+    # Cluster-wide defaults only — the Konnect PAT is NOT handled via
+    # substitute/substituteFrom at all: that mechanism requires the source
+    # Secret to sit in flux-system (same namespace as this Kustomization),
+    # which put a live copy of the real PAT in a shared, broadly-readable
+    # namespace. Rejected. The real konnect-auth Secret is materialized
+    # directly into the payments namespace instead (externalsecret.yaml, via
+    # External Secrets Operator + Vault) — never passes through flux-system.
+    substituteFrom:
+      - kind: ConfigMap
+        name: dataplane-template-defaults

dev/api-gateway/konnectextension.yaml

@@ -1,6 +0,0 @@
-# TODO: KonnectExtension referencing the Control Plane created by
-# konnect-platform/domains/payments/dev/ (by ID, not created here)
-apiVersion: konnect.konghq.com/v1alpha1
-kind: KonnectExtension
-metadata:
-  name: payments-dev

dev/api-gateway/kustomization.yaml

@@ -1,5 +0,0 @@
-apiVersion: kustomize.config.k8s.io/v1beta1
-kind: Kustomization
-resources:
-  - dataplane.yaml
-  - konnectextension.yaml

dev/api-gateway/policies-kustomization.yaml

@@ -0,0 +1,37 @@
+# Split from gateway-kustomization.yaml on purpose: different change
+# cadence (policies get tuned far more often than the Gateway itself gets
+# recreated) and different blast radius (a bad policy build/prune can't
+# touch the Gateway/DataPlane, and vice versa). Same GitRepository, same
+# domain namespace, different path.
+apiVersion: kustomize.toolkit.fluxcd.io/v1
+kind: Kustomization
+metadata:
+  name: payments-dev-api-gateway-policies
+  namespace: flux-system
+spec:
+  interval: 10m
+  sourceRef:
+    kind: GitRepository
+    name: k8s-platform
+  path: ./dataplane-globalpolicy-template
+  prune: true
+  postBuild:
+    substitute:
+      NAME: payments-dev
+      NAMESPACE: payments
+      # Looked up manually after gateway-kustomization.yaml's
+      # Gateway/GatewayConfiguration first reconciled — the operator
+      # auto-names the mirrored KonnectGatewayControlPlane with a random
+      # suffix, not derivable from NAME.
+      CONTROL_PLANE_REF_NAME: payments-dev-bz6vs
+      # Every audience valid anywhere in the payments domain — grows as the
+      # domain gains APIs (e.g. mcp-payments, if an MCP layer is ever added).
+      JWT_AUDIENCE_WHITELIST: '["payments-api"]'
+      # Local in-cluster Keycloak is the platform-wide IdP now (see
+      # ../../../STATUS.md sections 15/16), not dataplane-template-defaults'
+      # stale VPS value — confirmed reachable in-cluster before wiring this
+      # in, same pattern as catalog/customers.
+      OIDC_ISSUER: https://keycloak.sttlab.local/realms/classic-models
+    substituteFrom:
+      - kind: ConfigMap
+        name: dataplane-template-defaults