38083d7c3f
NotificationBell used a usePageVisible() subscription that re-rendered on
every visibilitychange without consuming the value. TanStack Query's
refetchIntervalInBackground:false already pauses polling; the extra
subscription was speculative generality. Dropped the import + call + JSDoc
reference; usePageVisible hook + test retained as a reusable primitive.
Also: alerts.test.tsx 'returns the server payload unmodified' asserted a
pre-plan {total, bySeverity} shape, but UnreadCountResponse is actually
{count}. Fixed mock + assertion to {count: 3}.