fix(interpreter): preserve executable script exit status

[skovranek]

Summary

• return an executable script's exit status to its parent command list
• add regression coverage for ; and && after executable scripts exit nonzero

Why

Executable scripts run in a subshell-like context, but their internal ExitError was rethrown after the script state was restored. That terminated the surrounding command list, so:

./fail.sh ; echo $?

never reached echo.

The script boundary now converts ExitError into a normal command result. This preserves the exit status while allowing the parent list to apply standard ; and && behavior.

## Verification

- pnpm vitest run src/interpreter/executable-script.test.ts

[vercel]

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[cramforce]

Looks good. Take a look at the CI runs