feat: implement per-event model attribution for enhanced event tracking

feat: implement Archive feature for past session management

feat(observability): instrument models, conductor, memory, ledger (Units 2-6)

feat: enhance agent personas and improve model performance tuning

feat: add optional mem0 cloud backend for memory index and update documentation

feat: unify model catalogue and self-hosted routing

feat: mem0 as a layered, derived semantic memory index