test: cover dry-run CLI flow

[terminalchai]

Closes #44

Summary

• add a CLI dry-run test for --dry-run --yes
• verify the installer path is skipped during dry-run
• assert [dry-run] output is printed for each supported tool on the mocked OS

Validation

• npx jest tests/dryRun.test.js ?
• npx jest --coverage ?? fails due existing repo issues unrelated to this test:
  • tests/scriptCoverage.test.js fails because tool script coverage is already out of sync for go
  • tests/installer.test.js has an existing assertion failure around bash call args
  • global coverage thresholds are already not met on the current baseline
• npx eslint src/ index.js tests/ ?? fails because ESLint cannot find a configuration file for the current command