feat: Set chat name (#4974)

Set chat name with `/name` so they appear in the codex resume page:


https://github.com/user-attachments/assets/c0252bba-3a53-44c7-a740-f4690a3ad405

codex-rs/tui/src/app_event.rs

@@ -85,6 +85,9 @@ pub(crate) enum AppEvent {
     /// Open the custom prompt option from the review popup.
     OpenReviewCustomPrompt,
 
+    /// Begin setting a human-readable name for the current session.
+    SetSessionName(String),
+
     /// Open the approval popup.
     FullScreenApprovalRequest(ApprovalRequest),
 }