Moves mic access, MediaRecorder handling, the pre-recording rolling
PCM buffer, and Whisper transmission processing out of live-atc.vue.
Keeps the internal AudioContext (prerecCtx) properly encapsulated —
the two external call sites that used to reach into it directly
(the lead-in-duration watcher and the SimBridge remote-PTT handler)
now go through small exposed functions instead.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
