Mem-Client: Actionable Error States

Mem-client error-state UX must remain actionable.

Scope:
- Enforce when changing error overlays/modals/toasts/recovery states in `domains/frontend/mem-client/src/**`.

Rules:
1) Error states should give users a clear recovery path (retry, dismiss, navigate, or explicit next step).
2) Avoid dead-end error states that trap users without action.
3) If recovery behavior changes, include validation evidence for the updated flow.

Review behavior:
- Return NOT APPROVED when changed error UX removes clear recovery behavior or introduces dead ends.
- Do not block cosmetic-only error UI tweaks that preserve behavior.