add Emailer and EmailFactory interfaces with laravel + fake impls

backend/app/Email/LaravelEmailFactory.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace App\Email;
+
+class LaravelEmailFactory implements EmailFactory
+{
+    public function __construct(
+        private string $confirmationUrlPrefix,
+    ) {}
+
+    public function makeConfirmationEmail(string $token): string
+    {
+        return "Confirm your email: {$this->confirmationUrlPrefix}{$token}";
+    }
+}