add email signup flow

backend/app/Email/LaravelEmailFactory.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace App\Email;
+
+use RuntimeException;
+
+class LaravelEmailFactory implements EmailFactory
+{
+    public function makeConfirmationEmail(string $token): string
+    {
+        $configuredFrontendUrl = config('app.frontend_url');
+        if (! is_string($configuredFrontendUrl)) {
+            throw new RuntimeException('FRONTEND_URL must be configured');
+        }
+
+        $frontendUrl = rtrim($configuredFrontendUrl, '/');
+        $confirmationUrl = $frontendUrl
+            .'/confirm-email?token='.urlencode($token);
+
+        return "Welcome to Attainly.\n\n"
+            ."Confirm your email and choose a password:\n"
+            ."{$confirmationUrl}\n\n"
+            .'This link expires in 10 minutes.';
+    }
+}