- Add FixChannelLayout() helper to AudioProcessor::Open() to fall back to a
default native channel layout when the input/output layout is unspecified,
custom, or has a zero mask. This prevents FFmpeg's abuffer/aformat filters
from rejecting 'channel_layouts=0x0' on Linux.
- Log audio processor open parameters, viewer audio queue state, and
AudioManager::PushToOutput device/stream status to help diagnose silent
playback on Linux.