- control_server: add Connection: close header + always return -1 after
HTTP response to force-close connection. Without this, lws_service()
blocks forever after the first POST /cmd, freezing the node process loop.
- passthrough: initialize read_index_ to runtime.headIndex when reader
is added (prevents TOO_EARLY errors on first read)
- passthrough: handle MXL_ERR_OUT_OF_RANGE_TOO_EARLY in addition to
TOO_LATE (both jump to head index)
- passthrough: use grain_info.index as writer index instead of separate
write_index_ counter (MXL writers must use TAI-based grain indices)
- passthrough: reduce grain read timeout from 100ms to 20ms for tighter
loop with LWS poll
- node_runner: add 'status' command handler that sends node status
back via control server