feat: Implement dark/light mode toggle and address linting issues

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.

src/routes/admin/route.tsx

@@ -98,8 +98,7 @@ function DashboardLayout() {
 
 	const isActive = (path: string) => {
 		const current = location.pathname;
-		if (path === "/admin")
-			return current === "/admin" || current === "/admin/";
+		if (path === "/admin") return current === "/admin" || current === "/admin/";
 		return current.startsWith(path);
 	};