Mem-Client: Behavioral Refactor Rollout Notes

Large behavioral mem-client refactors need rollout/migration notes.

Scope:
- Enforce when a mem-client refactor changes runtime behavior across multiple modules.

Rules:
1) PR description should include a short rollout or migration note for behavior-affecting refactors.
2) Mention key risk area(s) and how regressions would be detected/validated.
3) Prefer incremental safety checks when replacing existing behavior paths.

Review behavior:
- Return NOT APPROVED when a large behavioral refactor has no rollout/migration context or risk framing.
- Do not block small local refactors with no behavior change.