Mark a saved route as persisted (keeps it past the 30-min TTL)

Counts against the customer's per-plan persisted-route cap (max_saved_routes, or the per-customer override when set).

Supplying a notify block opts the route into monitoring: the route-monitor re-evaluates the route on a fixed interval and POSTs a route.alert webhook to notify.webhook_id whenever warnings appear on — or clear from — the route. Alerts are filtered to min_severity and types; an optional valid_from/valid_to window bounds when monitoring is active. The webhook body is { event: "route.alert", timestamp, data: { route_id, label, new_warnings[], cleared_warnings[] } }, HMAC-signed like every other Road511 webhook.