feat(managed_agents): add memory store cookbook

A guided tutorial showing how to give a Managed Agent a memory store so
it learns and recalls a customer's shopping preferences across separate
sessions. Covers store creation, the resources attachment with
per-attachment instructions, inspecting and seeding memories from your
own application, and combining a per-customer read-write store with a
brand-wide read-only store.

https://claude.ai/code/session_01VkfVPdiJTWVh6Vj5owqRXH

Author: claude