add Emailer and EmailFactory interfaces with laravel + fake impls

backend/tests/Fakes/FakeEmailFactory.php

@@ -0,0 +1,13 @@
+<?php
+
+namespace Tests\Fakes;
+
+use App\Email\EmailFactory;
+
+class FakeEmailFactory implements EmailFactory
+{
+    public function makeConfirmationEmail(string $token): string
+    {
+        return "confirm:{$token}";
+    }
+}