Vault credential background refresh enabled for mcp_oauth credentials

AI Impact Summary

HashiCorp Vault-based credentials for the mcp_oauth workflow now support automatic background renewal. This reduces the risk of service outages from expiring credentials, since applications won't need to explicitly renew tokens before expiry. Operators should verify Vault lease TTLs, renewal behavior, and the mcp_oauth auth configuration to ensure tokens can be renewed without user interaction, and monitor for renewal churn if credentials have short TTLs.