The game audio plays hot with no in-game control -- testers couldn't
hear voice chat without the Windows mixer (playtest night). The -/=
keys now step the OpenAL listener gain (the master scale every source
inherits) in 5% steps, clamped 0..150%, edge-detected in the per-frame
poll with a foreground guard; the value persists to content\volume.cfg
and reloads at boot (BT_AUDIO_VOLUME env still wins when set; default
stays 0.6). README updated.
Verified: volume.cfg 0.25 -> boot log "master gain=0.25"; key stepping
needs a live focused session (awaiting live verification).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
