Add realtime audio device config (#12849)

## Summary
- add top-level realtime audio config for microphone and speaker
selection
- apply configured devices when starting realtime capture and playback
- keep missing-device behavior on the system default fallback path

## Validation
- just write-config-schema
- cargo test -p codex-core realtime_audio
- cargo test -p codex-tui
- just fix -p codex-core
- just fix -p codex-tui
- just fmt

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/tui/src/lib.rs

@@ -63,6 +63,8 @@ mod app_backtrack;
 mod app_event;
 mod app_event_sender;
 mod ascii_animation;
+#[cfg(all(not(target_os = "linux"), feature = "voice-input"))]
+mod audio_device;
 mod bottom_pane;
 mod chatwidget;
 mod cli;
@@ -123,6 +125,7 @@ mod voice;
 mod voice {
     use crate::app_event::AppEvent;
     use crate::app_event_sender::AppEventSender;
+    use codex_core::config::Config;
     use codex_protocol::protocol::RealtimeAudioFrame;
     use std::sync::Arc;
     use std::sync::Mutex;
@@ -146,7 +149,7 @@ mod voice {
             Err("voice input is unavailable in this build".to_string())
         }
 
-        pub fn start_realtime(_tx: AppEventSender) -> Result<Self, String> {
+        pub fn start_realtime(_config: &Config, _tx: AppEventSender) -> Result<Self, String> {
             Err("voice input is unavailable in this build".to_string())
         }
 
@@ -186,7 +189,7 @@ mod voice {
     }
 
     impl RealtimeAudioPlayer {
-        pub(crate) fn start() -> Result<Self, String> {
+        pub(crate) fn start(_config: &Config) -> Result<Self, String> {
             Err("voice output is unavailable in this build".to_string())
         }