No test runner existed in the repo. Add vitest (node env, *.spec.ts
discovery) with a minimal config mirroring only the `@`→src alias, plus
`test`/`test:watch` scripts and a smoke test as a known-good baseline.
Precursor for the nostr-patterns review fixes (events store coordinate
keying #121, monotonic created_at #122), which ship with unit tests.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
