Free app_name on delete to prevent unique constraint collision

Appends '-deleted-{timestamp}' to app_name when instance is deleted,
so the name can be reused for new instances.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/Services/InstanceProvisionerService.php

@@ -209,7 +209,10 @@ public function delete(Instance $instance): void
         }
 
         AuditLog::record('deleted', $instance);
-        $instance->update(['status' => 'deleted']);
+        $instance->update([
+            'status' => 'deleted',
+            'app_name' => $instance->app_name . '-deleted-' . now()->timestamp,
+        ]);
     }
 
     public function updateEnvVars(Instance $instance, array $vars): void