Every request spawned a goroutine doing a 5s-timeout INSERT, unbounded
under load. Route entries through a buffered channel drained by a single
background writer that bulk-inserts with COPY every 128 entries or 2s.
logAccess is now a non-blocking send that drops on a full buffer, so the
request path never waits on the database.
Refs #76
unkinben
41f069bf96