Port Distances

Every cached destination reachable from port_id, with the distance for the chosen variant — paginated and sorted shortest-first.

"Show me everywhere a vessel can sail from Mundra and how far." For voyage analytics, rate-card builders, and port authorities. One metered call per request (not per row). The empirical via_* leak guard (known-issue #1) applies; the U-004 Cape estimate does not — this bulk listing reports measured distances only, so a via_cape with no cached value comes back distance_nm: null with an availability reason.