Clarify session exit messages (#40670)

## What changed

- Report `Session archived: <thread-id>` after successfully archiving the current session.
- Show the session ID when no resume hint is available, including for non-fatal exits.
- Keep deleted-thread exits distinct from successful archive exits.

## Testing

- Add coverage for archive lifecycle handling and exit-message formatting.

GitOrigin-RevId: 1812374e4c74fa1b3f11feb323de18a9dbff745b

codex-rs/tui/src/main.rs

@@ -38,9 +38,10 @@ fn main() -> anyhow::Result<()> {
                 eprintln!("ERROR: {message}");
                 true
             }
-            ExitReason::UserRequested | ExitReason::TurnInterrupted | ExitReason::ThreadRemoved => {
-                false
-            }
+            ExitReason::UserRequested
+            | ExitReason::Archived(_)
+            | ExitReason::TurnInterrupted
+            | ExitReason::ThreadRemoved => false,
         };
 
         let color_enabled = supports_color::on(Stream::Stdout).is_some();