fix(ui): сохранять точный выбор пира при экспорте WireGuard

lib/wg-export-peer.ts

@@ -0,0 +1,4 @@
+/** An explicit missing selection must never fall back to another peer. */
+export function selectWgExportPeer<T extends { id?: string; rosId?: string }>(peers: readonly T[], peerId?: string | null): T | undefined {
+  return peerId == null ? peers[0] : peers.find(peer => peer.id === peerId || peer.rosId === peerId)
+}