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/web/mod.rs

@@ -3,6 +3,7 @@ mod error;
 mod handlers;
 mod routes;
 mod static_files;
+mod uac_ws;
 mod ws;
 
 pub use audio_ws::audio_ws_handler;
@@ -10,4 +11,5 @@ pub use error::ErrorResponse;
 pub use routes::create_router;
 #[cfg(not(debug_assertions))]
 pub use static_files::StaticAssets;
+pub use uac_ws::uac_audio_ws_handler;
 pub use ws::ws_handler;