fix: fix or remove abandoned dependencies flagged by Renovate

[DevSecNinja]

Summary

The Renovate Dependency Dashboard (#3) flags the following dependencies as abandoned — they have not had a release for an extended period and may be unmaintained. We should either replace them or remove them.

Datasource	Package	Last Updated
npm	@testing-library/user-event	2025-01-21
npm	eslint-plugin-react	2025-04-03

Packages are marked abandoned by Renovate when they exceed the abandonmentThreshold since their last release. This is based on release inactivity, not an official deprecation notice.

Tasks

For each package, decide and act:

@testing-library/user-event

• Check whether it's still used in the test suite (src/**/*.test.*, src/test/).
• If unused → remove from devDependencies.
• If used → evaluate migrating to a maintained alternative or pinning/ignoring if no replacement is needed (the package is broadly stable).

eslint-plugin-react

• Confirm usage in the ESLint config (eslint.config.*).
• Evaluate whether it's still required given the current React/ESLint setup (eslint-plugin-react-hooks, eslint-plugin-react-refresh are already present).
• If still needed → keep and optionally suppress the abandonment warning via Renovate config; if not → remove it and its config references.

Notes

• If we consciously want to keep an "abandoned" package, suppress the warning in renovate.json5 rather than leaving the dashboard flag noisy.
• Run npm run lint and npm test after any dependency change to confirm nothing breaks.

Acceptance criteria

• Each abandoned package is either removed or an explicit decision to keep is documented (and the Renovate warning suppressed).
• Lint and tests pass.
• package.json / lockfile updated accordingly.

Refs #3