Live GCP provider tests

This project is deliberately excluded from UnifyEMPI.slnx. It writes synthetic resources and must run only against a short-lived, isolated Healthcare API R4 store supplied through GCP_FHIR_STORE, using Application Default Credentials.

dotnet test tests/UnifyEmpi.Storage.Gcp.LiveTests -c Release

Destroy the test store after the run. Never point this suite at a production or shared clinical store.