fix: fix CI test failures - vitest v1 compat and worker issues

- Pin vitest to v1.6.0 (v4 requires Node 20+, CI runs Node 18)
- Fix settings tests to not use process.chdir() (not supported in vitest workers)
- Fix retryWithBackoff to use fast delays in test mode (10/20/30ms vs 1s/3s/8s)
- Add npm test step to CI workflow

Author: thegreatalxx