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

web/src/i18n/en-US.ts

@@ -653,6 +653,8 @@ export default {
     otgNetworkDriver: 'Host Driver Mode',
     otgNetworkInterface: 'Bridge Interface',
     otgNetworkNone: 'None',
+    uacMic: 'USB Microphone',
+    uacMicDesc: 'Creates a virtual USB microphone on the target machine. Audio from your browser is streamed to the target.',
     otgDescriptor: 'USB Device Descriptor',
     vendorId: 'Vendor ID (VID)',
     productId: 'Product ID (PID)',