Remove webhook maintenance mode replay feature

This feature stored incoming webhooks during maintenance mode and replayed them
when maintenance ended. The behavior adds unnecessary complexity without clear
value. Standard approach is to let webhooks fail during maintenance and let
senders retry.

Removes:
- Listener classes that handled maintenance mode events and webhook replay
- Maintenance mode checks from all webhook controllers (Github, Gitea, Gitlab, Bitbucket, Stripe)
- webhooks-during-maintenance filesystem disk configuration
- Feature mention from CHANGELOG

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

config/filesystems.php

@@ -35,13 +35,6 @@ return [
             'throw' => false,
         ],
 
-        'webhooks-during-maintenance' => [
-            'driver' => 'local',
-            'root' => storage_path('app/webhooks-during-maintenance'),
-            'visibility' => 'private',
-            'throw' => false,
-        ],
-
         'public' => [
             'driver' => 'local',
             'root' => storage_path('app/public'),