- NotificationCenter closes on outside click (document listener, not an overlay
that the blurred header trapped) and no longer needs a second bell click.
- Toasts show a level-colored countdown bar and auto-dismiss faster (6s default).
- Hidden-video notifications carry structured meta so the center offers an in-app
'Find in feed' (jump to that channel's hidden videos) and a one-click 'Unhide',
working even after a reload when the live Undo callback is gone.
- Replace the toast store with a notification store: levels (info/success/
warning/error/fatal), requiresInteraction, and a persisted history.
- Move toasts to the top-right, styled per level, with manual dismiss.
- Add a bell in the header opening a Notification Center (history, unread badge,
'needs attention' vs info, clear all).
- Capture network failures and 5xx responses (api layer) and render crashes
(ErrorBoundary) as notifications.
- Sound + server-sourced events + per-account settings remain for 6b.
