Bug FixApril 18, 2026

eliminate nested button hydration warning in ConversationList

The room conversation row in ConversationList wrapped a nested dismiss <button> inside an outer <button>, which is invalid HTML and triggered React's validateDOMNesting hydration warning.
Converted the outer row to a div with role="button", tabIndex={0}, and onKeyDown handling Enter/Space so the nested dismiss button is valid and keyboard accessibility is preserved.
Added focus-visible:ring-2 on the row so keyboard focus remains visible.