fix(mail): voicemail notification missing attachment (#1013)

validate() checked subject/mainMessage before buildVariables() had
a chance to set them, causing RuntimeException for VoicemailNotification.
The fallback sendDirect() then sent the email without the attachment
because it never extracted recordingFile from the builder.

- Remove premature subject/mainMessage check from validate()
  (all builders populate these lazily in buildVariables at render time)
- Pass voicemail attachment in sendDirect() fallback path

Author: Alexey Portnov

src/Core/System/Mail/Builders/AbstractNotificationBuilder.php

@@ -337,10 +337,6 @@ public function validate(): void
         if (!filter_var($this->recipient, FILTER_VALIDATE_EMAIL)) {
             throw new \RuntimeException('Invalid email address: ' . $this->recipient);
         }
-
-        if (empty($this->subject) && empty($this->mainMessage)) {
-            throw new \RuntimeException('Either subject or main message must be set');
-        }
     }
 
     /**

src/Core/System/Mail/NotificationQueueHelper.php

@@ -22,6 +22,7 @@
 
 use MikoPBX\Core\System\BeanstalkClient;
 use MikoPBX\Core\System\Mail\Builders\AbstractNotificationBuilder;
+use MikoPBX\Core\System\Mail\Builders\VoicemailNotificationBuilder;
 use MikoPBX\Core\System\SystemMessages;
 use MikoPBX\Core\Workers\WorkerNotifyByEmail;
 
@@ -177,8 +178,13 @@ private static function sendDirect(AbstractNotificationBuilder $builder): bool
             LOG_INFO
         );
 
+        $attachmentFile = '';
+        if ($builder instanceof VoicemailNotificationBuilder) {
+            $attachmentFile = $builder->getRecordingFile();
+        }
+
         $service = new EmailNotificationService();
-        return $service->sendNotification($builder);
+        return $service->sendNotification($builder, attachmentFile: $attachmentFile);
     }
 
     /**