Add Sumly to a Laravel app

Set up Laravel 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/laravel; read it if anything below is unclear.

Steps:
1. In Sumly, open Visitors and copy your project's line.
2. Paste it into the `<head>` of your root layout: `resources/views/app.blade.php` with an Inertia starter kit (React, Vue or Svelte), or the layout your Livewire or Blade pages extend.
3. Deploy. Open the site and the visit shows on Visitors.

app.blade.php: Plain HTML in the head, next to Vite.
```
<head>
    <meta charset="utf-8">
    @vite(['resources/css/app.css', 'resources/js/app.ts'])
    @inertiaHead
    <script defer src="https://sumly.dev/s.js" data-site="sl_your_key"></script>
</head>
```

Checkout: With Cashier, pass the visitor to Stripe. Leave sumly_vid out of cookie encryption, so Laravel reads it as the script set it.
```
// bootstrap/app.php
->withMiddleware(function (Middleware $middleware) {
    $middleware->encryptCookies(except: ['sumly_vid']);
})

// where you start the checkout
$user->newSubscription('default', $price)
    ->withMetadata(['sumly_visitor_id' => request()->cookie('sumly_vid')])
    ->checkout();
```

Own domain: On any plan: two routes on your own site pass the script and its visits through to Sumly. Leave sumly/e out of CSRF.
```
// routes/web.php
use Illuminate\Http\Request;
use Illuminate\Support\Facades\Http;

Route::get('/sumly/s.js', fn () => response(Http::get('https://sumly.dev/s.js')->body())
    ->header('Content-Type', 'application/javascript')->header('Cache-Control', 'public, max-age=3600'));

Route::post('/sumly/e', function (Request $request) {
    Http::withHeaders([
        'User-Agent' => (string) $request->userAgent(),
        'X-Sumly-Client-IP' => (string) $request->ip(),
    ])->withBody($request->getContent(), 'text/plain')->post('https://sumly.dev/api/e');

    return response()->noContent();
});

// then, in the layout
<script defer src="/sumly/s.js" data-site="sl_your_key"></script>
```

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 Laravel'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.