detect terminal and include in request headers (#2437)

This adds the terminal version to the UA header.

codex-rs/core/src/lib.rs

@@ -49,6 +49,7 @@ pub(crate) mod safety;
 pub mod seatbelt;
 pub mod shell;
 pub mod spawn;
+pub mod terminal;
 pub mod turn_diff_tracker;
 pub mod user_agent;
 mod user_notification;