let ai hear and talk through the game

[Accusamus2065]

Summary

This PR adds game-audio routing support so OpenNeuro can hear in-game voice chat and speak back to players instead of being limited to the local microphone and speaker.

What was added:

• AudioIn: same port interface as Mic, but with a dynamic input-device dropdown
• AudioOut: same port interface as Speaker, but with a dynamic output-device dropdown
• RemoteAudioIn: same role as AudioIn, but receives audio from a remote WebSocket bridge
• RemoteAudioOut: same role as AudioOut, but sends audio to a remote WebSocket bridge
• src.lib.audio.remote_audio_server: FastAPI WebSocket bridge that runs on the game machine
• User docs for VB-Cable A+B and VRChat setup

Why

Before this change, OpenNeuro could only:

• read from the local mic
• write to the local speaker

That meant it could not:

• hear VRChat voice chat
• speak into the game's microphone path

This PR adds the missing local and remote routing pieces.

Local Same-Machine Setup

Use this when OpenNeuro and VRChat run on the same PC.

Recommended graph:
AudioIn -> VAD -> ASR -> LLM -> TTS -> AudioOut

OpenNeuro component settings:

1. Replace Mic with AudioIn.
2. Set AudioIn.device to CABLE-B Output.
3. Set AudioIn.sample_rate to 48000.
4. Set AudioIn.channels to 2.
5. Set AudioIn.frame_ms to 20.
6. Replace Speaker with AudioOut.
7. Set AudioOut.device to CABLE-A Input.
8. Set AudioOut.sample_rate to 48000.
9. Set AudioOut.channels to 1.

VRChat / Windows settings:

1. Install VB-Cable A+B.
2. In VRChat, set Microphone to CABLE-A Output.
3. VRChat does not expose a separate output-device selector here, so game output follows the Windows system playback device.
4. In Windows, set the default playback device to CABLE-B Input.
5. If you still want to hear the game locally, enable Listen to this device on CABLE-B Output and route it to your real headset/speakers.

Signal mapping:

• AI speech path: AudioOut -> CABLE-A Input -> CABLE-A Output -> VRChat microphone
• Game audio path: Windows default output / VRChat output -> CABLE-B Input -> CABLE-B Output -> AudioIn

Remote Two-Machine Setup

Use this when VRChat runs on one machine and OpenNeuro runs on another.

Game machine

1. Install VB-Cable A+B.
2. In VRChat, set Microphone to CABLE-A Output.
3. In Windows, set the default playback device to CABLE-B Input.
4. Start the bridge server:

cd backend
uv run python -m src.lib.audio.remote_audio_server

[github-actions]

Test Coverage

Target	Coverage	Covered Lines
Backend	94.20%	10254 / 10885
Frontend	89.02%	1467 / 1648