Add rewind feature

What version of the Codex App are you using (From "About Codex" dialog)?

Codex 26.212.1823

What subscription do you have?

Pro

What issue are you seeing?

The rewind/undo behavior available in the CLI is not present in the macOS app.

In CLI, it is possible to resume a previous state in a session by pressing Esc twice. In the macOS app, there does not appear to be an equivalent resume flow.

What steps can reproduce the bug?

1. Start a conversation/session in CLI.
2. Continue that session
3. Open Codex macOS app.
4. Attempt to rewind the same prior session/thread.

Observed: no rewind/undo option/flow is available in the app UI/controls.

What is the expected behavior?

The macOS app should provide parity with CLI rewind behavior (rewind a prior message in a thread and continue from saved context).