Return non-zero exit code on SIGINT (Ctrl+C) in exec mode

What version of Codex is running?

0.42.0

Which model were you using?

n/a

What platform is your computer?

Darwin 24.6.0 arm64 arm

What steps can reproduce the bug?

1. Run codex exec "foo"
2. Press CTRL+C before completion

What is the expected behavior?

Return a non-zero exit code eg: 130.
This allows scripts to handle any cleanup.

What do you see instead?

Zero exit code (ie: success)

Additional information

_No response_