Add deployment queue limit to prevent queue bombing

- Add configurable deployment_queue_limit server setting (default: 25)
- Check queue size before accepting new deployments
- Return 429 status for webhooks/API when queue is full (allows retry)
- Show error toast in UI when queue limit reached
- Add UI control in Server Advanced settings

Fixes #6708

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

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

app/Livewire/Project/Application/Rollback.php

@@ -30,7 +30,7 @@ class Rollback extends Component
 
         $deployment_uuid = new Cuid2;
 
-        queue_application_deployment(
+        $result = queue_application_deployment(
             application: $this->application,
             deployment_uuid: $deployment_uuid,
             commit: $commit,
@@ -38,6 +38,12 @@ class Rollback extends Component
             force_rebuild: false,
         );
 
+        if ($result['status'] === 'queue_full') {
+            $this->dispatch('error', 'Deployment queue full', $result['message']);
+
+            return;
+        }
+
         return redirect()->route('project.application.deployment.show', [
             'project_uuid' => $this->parameters['project_uuid'],
             'application_uuid' => $this->parameters['application_uuid'],