feat: implement actual webhook delivery

Implement full webhook delivery functionality:
- Create SendWebhookJob to handle HTTP POST requests
- Update WebhookChannel to dispatch webhook jobs
- Configure retry logic (5 attempts, 10s backoff)
- Update Test notification payload with success/message structure

Webhook payload structure:
{
  "success": true/false,
  "message": "notification message",
  "event": "event_type",
  "url": "coolify_dashboard_url"
}

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

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

app/Notifications/Test.php

@@ -116,8 +116,9 @@ class Test extends Notification implements ShouldQueue
     public function toWebhook(): array
     {
         return [
-            'event' => 'test',
+            'success' => true,
             'message' => 'This is a test webhook notification from Coolify.',
+            'event' => 'test',
             'url' => base_url(),
         ];
     }