findOneBy
exist
* refactor(backend): 存在確認の`findOneBy`を`exist`に置き換え * cleanup
* wip * wip * wip * wip * wip * Update ui.ts * wip * wip * wip * wip * wip * wip * wip * wip * Update CHANGELOG.md * wip * wip * wip * wip * 🎨 * wip * ✌️