Implementation report

Summary

Standardized crate README files as thin responsibility-boundary documents.

Rewrote existing stale README files to remove public-type inventories and outdated architecture claims.
Added concise README files for important crates that lacked them:
- client
- lint-common
- memory
- pod-registry
- pod-store
- secrets
- session-metrics
- tools
- workflow
- yoi
Each crate README now follows the same shape:
- Role
- Boundaries
- Design notes
- See also
README files link to maintained docs/design/ or docs/development/ docs instead of duplicating long design explanations.

All crates under crates/* have a README.
rg sweep for stale public-type headings, old crate title, accidental edit text, and old product names in crate README files => no output.
./tickets.sh doctor => doctor: ok
git diff --check => passed