Mem-Client: Keyboard and Focus Preservation

Interactive mem-client UI changes should preserve keyboard/focus usability.

Scope:
- Enforce when changing interactive components/controls in `domains/frontend/mem-client/src/**`.

Rules:
1) New/changed controls should remain keyboard reachable and operable.
2) Focus behavior should remain predictable after open/close/submit/error transitions.
3) Avoid interactions that are mouse-only when equivalent keyboard behavior is expected.

Review behavior:
- Return NOT APPROVED when UI interaction changes clearly break keyboard/focus behavior.
- Do not block non-interactive visual-only changes.