docs(site): governed memory — capability page, storage/PII statement and example

[amirkhan-ak-sf]

Part of #611.

Summary

Document governed memory on the docs site as it lands, following the end-user conventions (Live/Roadmap pills, Expected output panels, no issue numbers or verification narration in page text).

Changes

• A Memory capability page (Roadmap pill until code ships) explaining the three scopes (run, session, framework memory) and what each is for.
• A clear statement of which storage option is in use and what it means for PII at rest: governed store vs the framework's own store.
• Telemetry & cost: run ledger and memory span attributes.
• Typed refusals: the memory route section (if option A).
• Framework pages: the donkey.memory.<framework>() factory and its plain-framework equivalent.
• An example in the demos repo: a LangGraph agent that pauses, resumes from a checkpoint and reads its run ledger, using the simulator.
• Roadmap prose and Feature overview updated. Regenerate llms.txt / llms-full.txt.

Related

All sub-issues of this epic; docs conventions from #556.