Three bugs causing silent STT failure on Android:
1. AudioEncoder.opus produces an OGG container on Android but the file
was named .webm — faster-whisper rejected it due to format mismatch.
Changed to AudioEncoder.aacLc + .m4a (reliable on all Android versions).
Updated voice_api.dart to send audio/mp4 MIME type accordingly.
2. onError callback was never stored, so errors in _startListening() and
_handleSilence() were silently swallowed. Now stored as _onError and
called before exitVoiceMode() on any failure.
3. Amplitude stream can emit NaN or ±Infinity on some Android devices
during recorder initialisation. NaN < -40.0 is false, so silence was
never detected. Now treated explicitly as silence.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
bvandeusen