Simple large file uploads via presigned S3 URLs

[mnapoli]

Lambda limits request bodies to about 6 MB (roughly 4 MB of file once base64-encoded), so large files cannot go through the application.

This PR adds a helper to simplify S3 uploads: the browser asks the app for a presigned S3 URL, uploads the file straight to S3 under a temporary prefix, then sends the S3 key to the app, which validates it and moves the file to its final location.

Usage

Gate::define('uploadFiles', fn (User $user) => true);

import { upload } from 'bref-upload';
const { key } = await upload(file, { progress: (ratio) => console.log(ratio) });
// send `key` to the backend with the rest of the form

$validated = $request->validate([
    'file' => ['required', new UploadedToS3(extensions: ['pdf'], maxSize: 10 * 1024 * 1024)],
]);
Storage::copy($validated['file'], "documents/{$document->id}.pdf");

The bucket needs a lifecycle rule expiring tmp/ and a CORS rule allowing PUT from the app's origin. The Bref docs are updated in a separate PR.

Documentation: brefphp/bref#2181