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/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