NotificationsState

Immutable state holding isLoading, the merged notifications list, and an optional error. Exposes a derived unreadCount used by the bell badge.

1. const default is NotificationsState(isLoading: true, notifications: const []).
2. copyWith allows partial updates; error is intentionally pass-through (passing null clears).
3. unreadCount = notifications.where(!isRead).length — recomputed per watcher.

• unreadCount is O(n) — fine for ~50 items; if pagination grows, cache it on update.
• An empty list with a non-null error is a valid 'we tried, failed' state — UI should show retry, not skeleton.

• lib/src/features/shared/notifications/controllers/notifications_controller.dart:12 // NotificationsState

Stays in the same file as the controller — split if state grows independent concerns.