tui: remove the voice-input crate feature

## Why

`voice-input` is the only remaining TUI crate feature, but it is also a default feature and nothing in the workspace selects it explicitly. In practice it is just acting as a proxy for platform support, which is better expressed with target-specific dependencies and cfgs.

## What changed

- remove the `voice-input` feature from `codex-tui`
- make `cpal` a normal non-Linux target dependency
- replace the feature-based voice/audio cfgs with pure Linux-vs-non-Linux cfgs
- shrink the workspace-manifest verifier allowlist to remove the remaining `codex-tui` exception

codex-rs/tui/src/app_command.rs

@@ -121,10 +121,7 @@ impl AppCommand {
         Self(Op::RealtimeConversationStart(params))
     }
 
-    #[cfg_attr(
-        any(target_os = "linux", not(feature = "voice-input")),
-        allow(dead_code)
-    )]
+    #[cfg_attr(target_os = "linux", allow(dead_code))]
     pub(crate) fn realtime_conversation_audio(params: ConversationAudioParams) -> Self {
         Self(Op::RealtimeConversationAudio(params))
     }

codex-rs/tui/src/app_event.rs

@@ -313,10 +313,7 @@ pub(crate) enum AppEvent {
     },
 
     /// Persist the selected realtime microphone or speaker to top-level config.
-    #[cfg_attr(
-        any(target_os = "linux", not(feature = "voice-input")),
-        allow(dead_code)
-    )]
+    #[cfg_attr(target_os = "linux", allow(dead_code))]
     PersistRealtimeAudioDeviceSelection {
         kind: RealtimeAudioDeviceKind,
         name: Option<String>,

codex-rs/tui/src/app_event_sender.rs

@@ -63,10 +63,7 @@ impl AppEventSender {
         ));
     }
 
-    #[cfg_attr(
-        any(target_os = "linux", not(feature = "voice-input")),
-        allow(dead_code)
-    )]
+    #[cfg_attr(target_os = "linux", allow(dead_code))]
     pub(crate) fn realtime_conversation_audio(&self, params: ConversationAudioParams) {
         self.send(AppEvent::CodexOp(
             AppCommand::realtime_conversation_audio(params).into_core(),

codex-rs/tui/src/lib.rs

@@ -79,9 +79,9 @@ mod app_event;
 mod app_event_sender;
 mod app_server_session;
 mod ascii_animation;
-#[cfg(all(not(target_os = "linux"), feature = "voice-input"))]
+#[cfg(not(target_os = "linux"))]
 mod audio_device;
-#[cfg(all(not(target_os = "linux"), not(feature = "voice-input")))]
+#[cfg(target_os = "linux")]
 mod audio_device {
     use crate::app_event::RealtimeAudioDeviceKind;
 
@@ -151,9 +151,9 @@ pub mod update_action;
 mod update_prompt;
 mod updates;
 mod version;
-#[cfg(all(not(target_os = "linux"), feature = "voice-input"))]
+#[cfg(not(target_os = "linux"))]
 mod voice;
-#[cfg(all(not(target_os = "linux"), not(feature = "voice-input")))]
+#[cfg(target_os = "linux")]
 mod voice {
     use crate::app_event_sender::AppEventSender;
     use codex_core::config::Config;