free5GC's SMF UPI DELETE /upi/v1/upNodesLinks/{ref} panics on AN-node deletion via nil UPF dereference; unauthenticated, state-mutating

Summary free5GC's SMF mounts the UPI management route group without inbound OAuth2 middleware same root cause as the broader UPI auth gap reported in free5gc/free5gc887. On top of that, the DELETE /upi/v1/upNodesLinks/upNodeRef handler unconditionally dereferences upNode.UPF after the type-guarde...