Creating AVAudioEngine at singleton init time causes macOS to switch
Bluetooth headphones from A2DP (high quality) to HFP (headset) profile,
resulting in degraded audio quality even when Voice Wake is disabled.
This change makes audioEngine optional and only creates it when voice
recognition actually starts, preventing the profile switch for users
who don't use Voice Wake.
Fixes#30🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
5e8c8367f3