Mem-Client: No Deprecated Design-System Imports

New mem-client code should not introduce deprecated `@/design-system` imports.

Rationale:
- Preventing new deprecated imports keeps migration progress and avoids split design-system usage.

Scope:
- PR review policy for source files under `domains/frontend/mem-client/src/**`.

Trigger:
- A PR introduces new imports or re-exports from `@/design-system`.

Approval checks:
1) New `@/design-system` imports/re-exports are not introduced.
2) New design-system usage imports from `@/mds` when available.

Evidence:
- Diff of imports/re-exports shows no new `@/design-system` references.

Decision:
- Return NOT APPROVED when trigger is met and new deprecated imports are introduced.