Extract Ladill QR Plus as standalone app at qr.ladill.com.

Utility QR types only (URL, WiFi, link list, business, app download) with
SSO, Billing API integration, public /q resolver, and qr-plus:import for
platform migration. vCard and commerce types stay on the platform.

Co-authored-by: Cursor <cursoragent@cursor.com>

config/mailbox.php

@@ -0,0 +1,9 @@
+<?php
+
+return [
+    // Consumer config for the platform Mailbox provisioning API (§4). Mail infra
+    // (Postfix/Dovecot via mail DB + pools) lives on the platform; this app
+    // provisions through the API. The user is identified by public_id.
+    'api_url' => env('MAILBOX_API_URL', 'https://ladill.com/api/mailboxes'),
+    'api_key' => env('MAILBOX_API_KEY_EMAIL'),
+];