refactor: move backend in apps/backend

apps/backend/routes/channels.php

@@ -0,0 +1,7 @@
+<?php
+
+use Illuminate\Support\Facades\Broadcast;
+
+Broadcast::channel('App.Models.User.{id}', function ($user, $id) {
+    return (int) $user->id === (int) $id;
+});