test(openapi): GET /v1/customer/search 200 envelope shape is unpinned

[CryptoJones]

The OpenAPI spec declares the full envelope for /v1/customer/search (message, q, companyId, count, limit, offset, customers: Customer[]) but tests/api/openapi.test.js has no assertion pinning the shape. A future "cleanup" that drops a field from the spec would silently regress SDK code-gen output.

Fix: pin the seven properties + the Customer items $ref.

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