voice transcription (#3381)

Adds voice transcription on press-and-hold of spacebar.


https://github.com/user-attachments/assets/85039314-26f3-46d1-a83b-8c4a4a1ecc21

---------

Co-authored-by: Codex <199175422+chatgpt-codex-connector[bot]@users.noreply.github.com>
Co-authored-by: David Zbarsky <zbarsky@openai.com>

codex-rs/core/src/features.rs

@@ -138,6 +138,8 @@ pub enum Feature {
     CollaborationModes,
     /// Enable personality selection in the TUI.
     Personality,
+    /// Enable voice transcription in the TUI composer.
+    VoiceTranscription,
     /// Prevent idle system sleep while a turn is actively running.
     PreventIdleSleep,
     /// Use the Responses API WebSocket transport for OpenAI by default.
@@ -627,6 +629,12 @@ pub const FEATURES: &[FeatureSpec] = &[
         stage: Stage::Stable,
         default_enabled: true,
     },
+    FeatureSpec {
+        id: Feature::VoiceTranscription,
+        key: "voice_transcription",
+        stage: Stage::UnderDevelopment,
+        default_enabled: false,
+    },
     FeatureSpec {
         id: Feature::PreventIdleSleep,
         key: "prevent_idle_sleep",