feat(v0.10.5): Notifications complètes — F551-F555
F555: Backend pagination/filter GetNotifications (type, page, limit) + frontend pagination
F551: WebSocket real-time — backend inject chat hub, send on CreateNotification; frontend useChat invalidates
F553: Quiet hours — migration 132, CreateNotification skips push/WS, UI in PushPreferencesSection
F554: Notification grouping — migration 133, group_key/actor_count for like/comment, UI format
F552: Weekly digest — migration 134, NotificationDigestWorker, email template, prefs UI
Acceptance: no gamification notif; defaults unchanged; individual toggles for marketing
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