The peer listener died with "Too many open files (os error 24)" on any
long-lived non-daemon session: only the daemon raised RLIMIT_NOFILE, and
peer sockets were unbounded — no idle reaping, no deadlines on accepted
transfer streams, and one peer could hold two connections under split
registry identities.
- raise the open-file limit at the top of run(), for every entry point,
and warn from Client::connect when the soft limit is below 1024
- reap peer control connections idle for five minutes; a clean
disconnect no longer discards the peer's queued uploads
- give listener-supplied download streams and upload serving the same
read/write deadlines dialled sockets already had
- register inbound peers under their plain username so the registry
holds one connection per peer, and announce them like pierced ones
- hold the registry lock across actor spawn + insert and surface
thread-spawn failure, so an instantly-dead peer cannot leave a
zombie entry