Move terminal module to terminal-detection crate (#15216)

- Move core/src/terminal.rs and its tests into a standalone
terminal-detection workspace crate.
- Update direct consumers to depend on codex-terminal-detection and
import terminal APIs directly.

---------

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

codex-rs/cli/src/main.rs

@@ -50,7 +50,7 @@ use codex_core::config::edit::ConfigEditsBuilder;
 use codex_core::config::find_codex_home;
 use codex_core::features::Stage;
 use codex_core::features::is_known_feature_key;
-use codex_core::terminal::TerminalName;
+use codex_terminal_detection::TerminalName;
 
 /// Codex CLI
 ///
@@ -1049,7 +1049,7 @@ async fn run_interactive_tui(
         interactive.prompt = Some(prompt.replace("\r\n", "\n").replace('\r', "\n"));
     }
 
-    let terminal_info = codex_core::terminal::terminal_info();
+    let terminal_info = codex_terminal_detection::terminal_info();
     if terminal_info.name == TerminalName::Dumb {
         if !(std::io::stdin().is_terminal() && std::io::stderr().is_terminal()) {
             return Ok(AppExitInfo::fatal(