``logout`` calls ``clearAtomStorage(systemConfigAtom)`` which sets the
atom to ``null``, and on a fresh SPA login (no full reload)
``app.tsx``'s ``fetchSystemConfig`` doesn't re-run, so consumers that
read ``systemConfig.xxx`` directly crash with "Cannot read properties
of null". A hard refresh masks the bug. Add optional chaining at the
read sites (grafana url / dashboard uids, showMonitoring) so the
contract stays robust regardless of how the atom is reset.
