fix(openai): expose only client-fault streaming errors

Forward an upstream failure to Responses websocket and SSE clients only when the request itself is at fault. Credential, quota and transport failures now close the stream silently so the client reconnects and retries; a fresh websocket carries no server-side transcript, so reconnecting already implies a full context resend and needs no extra close-code signal.

Classify the failure from the upstream error body instead of the attached status. Codex reports the same cyber_policy rejection as 400 on the stream error path and as 502 through the websocket disconnect channel, so a status-only whitelist hid most of them. Treat cyber_policy as a request error so it stops credential failover without suspending the credential, and treat 413 as request-scoped because a payload that exceeds the upstream frame limit fails identically on every credential and would otherwise burn the whole pool.

Report an unroutable model as 400 invalid_request_error instead of 502 so streaming clients receive an actionable message instead of retrying forever. Keep the upstream reason in the request-log websocket timeline when the client only observes a closed connection, and stop logging expected connection-teardown races as warnings.