feat: UAC USB microphone passthrough

- Add UAC1 gadget function (ConfigFS) with optimized endpoint config
- Browser mic capture with Opus encoding via WebCodecs AudioEncoder
- WebSocket audio transport (Opus 64kbps, 100x bandwidth reduction vs raw PCM)
- aplay subprocess for reliable PCM playback to USB gadget
- Settings toggle + ActionBar mic button (hidden when UAC disabled)
- Dynamic PCM device resolution (/proc/asound)
- c_chmask=0 + req_number=4 fixes DWC3 composite isochronous endpoint issue

src/audio/mod.rs

@@ -11,6 +11,8 @@ pub mod monitor;
 pub mod recovery;
 pub mod streamer;
 pub mod types;
+pub mod uac_streamer;
+pub mod uac_websocket;
 
 pub use capture::{AudioCapturer, AudioConfig, AudioFrame};
 pub use controller::AudioController;