feat: include cwd in notify payload (#5415)

Expose the session cwd in the notify payload and update docs so scripts
and extensions receive the real project path; users get accurate
project-aware notifications in CLI and VS Code.

Fixes #5387

codex-rs/core/src/codex.rs

@@ -1715,6 +1715,7 @@ pub(crate) async fn run_task(
                         .notify(&UserNotification::AgentTurnComplete {
                             thread_id: sess.conversation_id.to_string(),
                             turn_id: sub_id.clone(),
+                            cwd: turn_context.cwd.display().to_string(),
                             input_messages: turn_input_messages,
                             last_assistant_message: last_agent_message.clone(),
                         });