Add Sumly to a React Router or Vite React app

Set up React Router and Vite for Sumly in this project.

Sumly (https://sumly.dev) shows revenue next to the visits and app users it came from. The full guide is https://sumly.dev/install/react-router; read it if anything below is unclear.

Steps:
1. In Sumly, open Visitors and copy your project's line.
2. With React Router's framework mode, paste it into the `<head>` of the `Layout` in `app/root.tsx`, after `<Links />`. In a plain Vite app, paste it into the `<head>` of `index.html` at the project's root.
3. Deploy. Open the app and the visit shows on Visitors; each route you go to counts as a page view.

app/root.tsx: In the head the root layout renders for every route.
```
export function Layout({ children }: { children: React.ReactNode }) {
  return (
    <html lang="en">
      <head>
        <meta charSet="utf-8" />
        <Meta />
        <Links />
        <script defer src="https://sumly.dev/s.js" data-site="sl_your_key"></script>
      </head>
      <body>
        {children}
        <ScrollRestoration />
        <Scripts />
      </body>
    </html>
  );
}
```

index.html: A plain Vite app: the page Vite builds from.
```
<!doctype html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <script defer src="https://sumly.dev/s.js" data-site="sl_your_key"></script>
  </head>
  <body>
    <div id="root"></div>
    <script type="module" src="/src/main.tsx"></script>
  </body>
</html>
```

Keep in mind: The Layout also draws the error page, so keep the line there rather than in a route: errors then count as visits too. With a nonce-based content security policy, allow the script's address (or your own domain's) in it.

How to work:
- Look at how this project is built first, and fit the code to its framework and its way of doing things; the examples above are a starting point, not something to paste as is.
- Steps that happen in a dashboard (Sumly, or React Router and Vite's own) are mine: tell me exactly what to click, then wait for me.
- Keys the code needs belong in environment variables, never in the code or the repository. Never ask me to paste a secret key into this chat; tell me which variable to set.
- Change only what this needs, show me the changes before you commit, and tell me how to check that it works.
- sl_your_key stands for the project's public key; it is on the Visitors page in Sumly. Ask me for it.