Notifications

• GET/notifications
  List notificationsList notifications addressed to the authenticated user, newest first. Deleted notifications are excluded. With `unreadFirst=true`, unread notifications come first and are ordered newest-first within that group (useful for a header dropdown).
• GET/notifications/unread-count
  Unread notification countReturn just the authenticated user's unread notification count. A lightweight endpoint for rendering a badge.
• PUT/notifications/:id/read
  Mark a notification as readMark the given notification as read. Idempotent — calling it on an already-read notification succeeds. Returns 404 for notifications owned by another user or already deleted.
• PUT/notifications/read-all
  Mark all notifications as readMark every unread notification of the authenticated user as read. Returns how many were updated.