Drift-audit Group 7: learned_summary, observations_raw, and
observations_updated_at were populated by the curator/LLM-profile machinery
removed in the Phase-8 pivot. Nothing has written them since and the profile
API returned permanently-empty fields. Remove them from the model + to_dict
and drop the columns (migration 0062). Verified zero frontend/backend/test
consumers.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
