This commit introduces a functional dark/light mode toggle by integrating
`next-themes` with the application. It configures `ThemeProvider` in
`src/frontend.tsx` and sets `darkMode: 'class'` in `tailwind.config.js`.
Additionally, this commit resolves several linting and parsing issues
found in `src/index.ts`.
This commit also includes other pre-existing modifications and new
components within the project's working directory that were not
specifically part of the dark mode or linting tasks.
