Chat turns now flow through the bounded inference queue: FIFO with
configurable depth (TIMMY_AGENT_MAX_QUEUE_DEPTH) and concurrency
(TIMMY_AGENT_MAX_CONCURRENT_TURNS), sanitized overload/timeout
fallbacks, browser-disconnect cancellation via AbortSignal, and child
process SIGTERM/SIGKILL teardown so no Hermes subprocess survives a
cancelled turn.
