generate random kana on click

[sheleoni]

On /play route, generate random kana character, and click the kana character to generate the next random character.

Organising components: https://nextjs.org/docs/app/building-your-application/routing/colocation

• unlike page router, app router does not make files routable unless it is named page.js. So we can put the <QuestionWord /> component under /src/app/play/QuestionWord.tsx