FU-06 (Audio Bridge STT orchestration): one download, two extractions — takes already-downloaded video bytes and extracts bounded mono 16kHz PCM WAV via the loopback broker's new mode=audio operation, sharing the exact same queue/deadline/byte budgets as the frame path. Dual opt-in (operator setting default false + per-request), only reaches the STT call when both are on.
Rebased onto the tip after sibling #12011 (subtitle mode) landed first, both touching the same broker route/client — combined additively so frames/audio/subtitles all share the one extractionQueue singleton. Re-validated: 59/59 focused tests pass.