Allow relative links in FilamentPHP's RichEditor Field.

AppServiceProvider.php

<?php

namespace App\Providers;

use Filament\Facades\Filament;
use Illuminate\Contracts\View\View;
use Illuminate\Support\ServiceProvider;

class AppServiceProvider extends ServiceProvider
{
    public function register() {}

    public function boot()
    {
        Filament::registerRenderHook(
            'body.start',
            fn(): View => view('admin.trix-editor-url-workaround'),
        );
    }
}

trix-editor-url-workaround.blade.php

<script>
    // This hooks into attribute changes to the Trix "link field" and
    // changes the type from "url" to "text" to allow for relative links.
    document.addEventListener("DOMContentLoaded", function () {
        const observer = new MutationObserver(() => {
            document
                .querySelectorAll('[data-trix-input][name=href]')
                .forEach(el => el.type = "text");
        });

        document
            .querySelectorAll('.trix-dialog--link')
            .forEach(el => observer.observe(el, {attributes: true}));
    });
</script>