test: add CLI output snapshots

[terminalchai]

Closes #46

Summary

• add snapshot coverage for the CLI banner
• add snapshot coverage for --list output formatting
• add snapshot coverage for the completion footer message

Validation

• npx jest tests/output.test.js ?

Notes

• this PR is scoped to the new snapshot test file and generated snapshots only
• full repo validation is still not green on the current baseline outside this change:
  • npx jest --coverage fails because existing tests already fail in tests/scriptCoverage.test.js and tests/installer.test.js, and current coverage thresholds are not met
  • npx eslint src/ index.js tests/ fails because ESLint cannot find a configuration file for the current command path in the repo state checked here