Mem-Client: State Mutation Boundaries

Keep mem-client state mutations within clear store/action boundaries.

Scope:
- Enforce when changing client state management logic in `domains/frontend/mem-client/src/**`.

Rules:
1) Avoid ad-hoc cross-module mutation that bypasses established store/action update paths.
2) Prefer explicit store actions/update helpers over scattered direct mutation.
3) Refactors should preserve clear ownership of writable state.

Review behavior:
- Return NOT APPROVED when new changes introduce unclear or unsafe mutation patterns.
- Do not block harmless local refactors that keep mutation boundaries intact.