harden core plumbing and move server bootstrap out of entrypoints

destroy the upgraded websocket on all exit paths so failed fallbacks stop leaking connections.
serialize ring log writes behind a lockfile, isolate test-models logs.
one keep alive upstream agent with a single retry on real network errors only.
readbody drains past the cap and cuts sockets at four times the limit.
drop unused chat.send bridge exports, unify client ip on trusted proxies.
extract gateway server factory, banner, health handler, process guards.