Prune closed channels from store on definitive ChannelNotOpen #4

The expiry-reclaim sweep (crates/server/src/reclaim.rs, DecdnTreasury::reclaim_expired in crates/server/src/treasury.rs) calls reclaimExpired via a simulated .call() first and treats any revert as Ok(false) (leave the row). A channel closed via a non-reclaim path (cooperative/dispute close) returns ChannelNotOpen forever, so its store row is never pruned — unbounded but harmless (a cheap retried eth_call each tick).

Fix: distinguish a definitive ChannelNotOpen/closed state from "not yet expired" and drop the row when the channel is provably gone (e.g. a settlement-event watcher, or a getChannel status check).

v1-acceptable per final review; follow-up hardening.