W-08: Add CHECK constraint on notifications.type (migration 044) with
defensive pre-check and matching __table_args__ on model.
W-05: Auto-detach umbral contact before Person delete — nulls out
connection's person_id so the connection survives deletion.
W-01: Add PUT /requests/{id}/cancel endpoint with atomic UPDATE,
silent notification cleanup, and audit logging. Frontend: direction-aware
ConnectionRequestCard, cancel mutation, pending requests section on
PeoplePage with incoming/outgoing subsections.
W-06: Convert useNotifications to context provider pattern — single
subscription shared via NotificationProvider in AppLayout. Adds
refreshNotifications convenience function.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>