Chains are real Xray hops: a chain-<code> inbound + outbound + routing rule on the
entry node and a relay-<code> client on the exit node, reconciled by sync_node with
config test, port check, rollback on a failed restart and a per-node lock.
Admin API gets chains CRUD/probe/check, node latency, audit log (middleware, no request
bodies), users list with subscription counters and a csv export that neutralises formulas.
