Header-grade notifications panel. Slot-trigger Popover the consumer wraps around their own Bell button. Filter tabs (All/Unread), Today/Earlier groups, category-coloured accent bars, hover-dismiss, mark-all-read, slide-in animation. Slot receives `unreadCount` so the trigger can show a badge.
npx shadcn@latest add https://uipkge.dev/r/react/notifications-popover.jsonnotifications-popover