XY-1069: [ELF AMK P3] Add mem0/OpenMemory and Letta memory-history/core-archive adapters

[yvette-carlisle]

Summary

• Add the real-world memory mem0/OpenMemory/Letta adapter benchmark task.
• Add same-corpus mem0 SDK history/export evidence and typed blockers for OpenMemory UI/export and Letta core/archive readback.
• Add the checked-in benchmark report, snapshot, and docs references while preserving hosted/product parity boundaries.

Validation

• cargo make real-world-memory-mem0-openmemory-letta
• cargo make fmt
• cargo make lint-fix
• cargo make checks

Review

• Independent Decodex read-only review checkpoint: clean for HEAD ed3dabd.