Add wake lock to prevent screen sleep on mobile

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

dashcam.html

@@ -400,7 +400,15 @@ function toggleUnit() {
   document.getElementById('big-speed-unit').textContent=unit;
 }
 
-window.addEventListener('DOMContentLoaded', () => startDashcam());
+let wakeLock = null;
+async function requestWakeLock() {
+  try { wakeLock = await navigator.wakeLock.request('screen'); } catch(e) {}
+}
+document.addEventListener('visibilitychange', () => {
+  if (document.visibilityState === 'visible') requestWakeLock();
+});
+
+window.addEventListener('DOMContentLoaded', () => { startDashcam(); requestWakeLock(); });
 
 function toggleFullscreen() {
   const app=document.getElementById('app'), btn=document.getElementById('fs-btn');