- Add /notifications inbox with mark-read and mark-all-read actions
- Respect mutedAll/mutedTypes preferences when creating notifications
- Add View all link and Discord request label to the notifications bell
- user-notifications collection (per-user inbox, owner-scoped read)
- notifyUser() fire-and-forget helper + notification label mapping
- NotificationsBell in the site header with 30s polling, unread badge,
mark-read on click, and "Mark all read"
- markNotificationsRead / markAllNotificationsRead server actions
