Build customers-api REST layer (Layer 3), mirroring catalog-api

8 routes over Customer + orders/payments sub-resources, proxying to
classic-models-api. openid-connect with RFC 8693 token exchange to
classic-models-api audience, rate-limiting, proxy-cache, audit-log —
same plugin set and structure as catalog-api's REST surface.

Not deployed: dev/gitrepository.yaml points at a gitea repo that
doesn't exist yet (kong-customers-api.git, 404). No MCP layer yet
either, unlike catalog-api.

dev/flux-kustomization.yaml

@@ -0,0 +1,37 @@
+apiVersion: kustomize.toolkit.fluxcd.io/v1
+kind: Kustomization
+metadata:
+  name: customers-dev-api
+  namespace: customers
+spec:
+  interval: 10m
+  sourceRef:
+    kind: GitRepository
+    name: customers-api-dev
+  path: ./kong
+  prune: true
+  dependsOn:
+    - name: customers-dev-api-gateway
+      namespace: flux-system
+  postBuild:
+    substitute:
+      NAME: customers-dev
+      NAMESPACE: customers
+      CONTROL_PLANE_REF_NAME: customers-dev-tw8tn
+      BACKEND_HOST: classic-models-api.classic-models.svc.cluster.local
+      OIDC_ISSUER: https://keycloak.sttlab.local/realms/classic-models
+      API_AUDIENCE: '["customers-api"]'
+      # Unused today — same dead variable already present in catalog-api's
+      # flux-kustomization.yaml (no file under kong/rest/ or kong/mcp/
+      # actually reads API_SCOPES_REQUIRED). Kept for parity; fix in both
+      # places together if this ever gets wired up for real.
+      API_SCOPES_REQUIRED: '["customers:read"]'
+      BACKEND_AUDIENCE: '["classic-models-api"]'
+      BACKEND_SCOPES: '[]'
+      API_RATE_LIMIT_MINUTE: "60"
+      AUDIT_LOG_ENDPOINT: http://audit-log-collector.observability.svc.cluster.local/logs
+      REST_HOSTNAME: customers-dev.sttlab.local
+      TOKEN_EXCHANGE_CLIENT_ID: kong-token-exchange-broker
+    substituteFrom:
+      - kind: Secret
+        name: customers-token-exchange-broker