Support voice-aware configuration and version-skew builds (#39953)

## What changed

- Add `chat.toggle_voice_mute` to the configurable TUI keymap and generated configuration schema.
- Let the exec-server version-skew harness build the voice-enabled CLI on Debian-like Linux hosts without preinstalled development metadata by assembling a temporary package sysroot.
- Preserve the existing build path on other Linux environments when the Debian package tools are unavailable.

## Testing

- Add a shell test that verifies a non-Debian Linux environment without voice metadata still proceeds to the Cargo build.

GitOrigin-RevId: 95c5ebc3f85d152a5217dee561286f2be662f79a

codex-rs/config/src/tui_keymap.rs

@@ -123,6 +123,8 @@ pub struct TuiGlobalKeymap {
 #[serde(deny_unknown_fields)]
 #[schemars(deny_unknown_fields)]
 pub struct TuiChatKeymap {
+    /// Toggle the microphone in an active voice conversation.
+    pub toggle_voice_mute: Option<KeybindingsSpec>,
     /// Interrupt the active turn.
     pub interrupt_turn: Option<KeybindingsSpec>,
     /// Decrease the active reasoning effort.