Locks down the resume path from the parent commit:
- Every AudioContext is tracked at construction (the wrap is active)
- unlockAudio() resumes all suspended tracked contexts in parallel
- Idempotent: repeated calls do not re-resume
- Contexts created after unlock are not re-resumed by a second call
- resume() rejections are swallowed — one bad context doesn't block others
- installAudioUnlock() is idempotent (the _installed gate works)
The unlock path was the fix for the "click does nothing" bug on Linux
Firefox/Chrome and Android Chrome, where AudioContexts created before a
user gesture stay suspended — decodeAudioData hangs → WaveSurfer's ready
never fires → the play button never enables. Without this test, breaking
the gesture wiring silently regresses every non-macOS browser.
Adds the __resetForTesting() export so the unlock can be exercised
repeatedly against the same module instance (the unlock is meant to be
a one-shot per page load).
