S6: Off-site notifications for berth events

[xishell]

Persona

Harbor master + Berth tenant

User outcome

As a harbor master off-site, I get email/push notifications for the berth events I care about. As a berth tenant, I get notified if a boat is at my berth without authorization.

Off-site responsiveness — the dashboard panel (S5) only helps when staff are at it.

Acceptance Criteria

• Harbor master can opt in/out of notifications per event type (arrival, departure, turned green, turned red)
• Berth tenant receives notification only when their berth turns occupied without authorization
• Notifications dispatched via Resend
• No duplicate notifications for the same ongoing event
• Notification preferences persist per user
• Tenant is notified of an approaching return-date deadline at a configurable lead time