#995 LLM provider api key by secret_id never resolves: engine.tools.secrets does not exist

EARS: When tools.llm.call is given a secret_id, the system shall resolve the API key from the calling tenant's secret store and fail the call if it does not resolve. FOUND in #924: docker/highway-core/engine/tools/llm/core/providers.py _get_api_key_from_secret_manager imports engine.tools.secrets (type: ignore[import-not-found]); in highway-api that import raises ModuleNotFoundError, the except logs a warning and returns None, so the key silently falls back. Fix in core using engine.security.secret_store.TenantSecretStore (secrets/<uuid> + scope check), with a red test.