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/handlers/config/mod.rs

@@ -15,6 +15,8 @@ mod redfish;
 mod rtsp;
 mod rustdesk;
 mod stream;
+#[cfg(unix)]
+mod uac;
 mod usb_update;
 pub(crate) mod video;
 mod vnc;
@@ -40,6 +42,8 @@ pub use rustdesk::{
     regenerate_device_password, start_rustdesk_service, stop_rustdesk_service,
     update_rustdesk_config,
 };
+#[cfg(unix)]
+pub use uac::{get_uac_config, update_uac_config};
 pub use stream::{get_stream_config, update_stream_config};
 pub use video::{get_video_config, update_video_config};
 pub use vnc::{