The Exit Codes table in the CLI reference only listed 0 and 2, but the
CLI also exits with 1 on fatal errors (missing environment variables,
Docker unavailable, invalid config file, diff-scope resolution failure,
or an unhandled exception). It also implied exit 0 means no
vulnerabilities were found, which is only true in headless mode -
interactive runs always exit 0 regardless of findings.
Document exit code 1 and clarify the two cases for exit 0.
