Adds `secret_values` param to `WorkflowResponseConverter.__init__` and a
`_redact` helper that delegates to `redact_secret_values` from
`core.workflow.secret_scrub`. Applies redaction to event-sourced
inputs/process_data/outputs in all four stream builders:
`workflow_node_finish_to_stream_response`,
`workflow_node_retry_to_stream_response`,
`workflow_finish_to_stream_response`, and
`workflow_pause_to_stream_response`. The `workflow_run.outputs_dict` path
(reconnect/resume) is intentionally untouched (already redacted by Plan 2).
Empty registry is a strict no-op, so existing tests pass unchanged.
Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
