* refactor: remove dead code and clarify observations vs mental models
- Delete engine/mental_models/ module (stale Pydantic models with wrong
schema, describing an old design where mental models were directives;
had no importers outside itself)
- Remove unused imports in api/http.py (acquire_with_retry, Observation)
- Remove unused Pydantic models in api/http.py (BanksResponse,
ObservationEvidenceResponse)
- Add clarifying NOTE to consolidation/consolidator.py distinguishing
observations (auto-generated bottom-up) from mental models (user-defined
pinned reflections refreshed via reflect)
* chore: run generate scripts after dead code removal
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