[Web] Add Mailcow\ class structure and imapsync module classes

data/web/inc/lib/mailcow/Imapsync/Http/OAuthException.php

@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Mailcow\Imapsync\Http;
+
+use RuntimeException;
+
+/**
+ * A failed OAuth request. The message is safe to store and show: "HTTP <code>" plus the provider's
+ * error fields, or a fixed text; never a raw response body or curl details.
+ */
+class OAuthException extends RuntimeException
+{
+}