Remove unused jsdom dependency; drop orphan assets/screenshot.png

[veillette]

Summary

Spawned from Code Review #1 (Repository structure / unused deps).

1. jsdom is listed in package.json devDependencies but Vitest uses environment: "happy-dom" only. Nothing imports jsdom directly (it appears only as an optional peer of Vitest in the lockfile). Safe to remove unless something external relies on it.
2. assets/screenshot.png is tracked in git but never referenced from README, docs, CI, or public/. Either wire it up (e.g. README / Pages) or delete it. Prefer public/ for static assets the app or docs serve.

References

• package.json
• vitest.config.ts
• assets/screenshot.png