Add guarded reboot control

public/assets/wakelock.js

@@ -55,7 +55,11 @@
         job.catch(error => {
             wanted = false;
             wakeLock = null;
-            alert(error.message || 'WakeLock failed');
+            const alertFn = window.customAlert || (() => Promise.resolve());
+            alertFn(error.message || 'WakeLock failed', {
+                title: 'WakeLock 오류',
+                danger: true,
+            });
             render();
         });
     });