fix(wakelock): screen-saver prevention breaks after Fire TV app-switch

[Copilot]

wakelock.js silently stopped preventing the screen saver after the user switched away from and returned to the guide page on Fire TV / Silk Browser. Two independent bugs:

Bugs fixed

• NoSleep video never resumed — browsers pause <video> elements when the page is hidden. The old handler guarded on !noSleepVideo (always false once the element was created), so the canvas-stream stayed paused for the rest of the session.

• Wake Lock sentinel release-event race — the browser releases the sentinel asynchronously on hide. If the release event fires after the page-visible visibilitychange, wakeLockSentinel is still non-null at the check and re-acquisition is skipped, leaving the lock permanently dropped.

Changes

• static/js/wakelock.js — rewrote the visibilitychange handler with three branches:

  State on page-show	Action
  NoSleep video exists and is paused	video.play()
  Wake Lock in use, sentinel gone	requestWakeLock()
  Sentinel still exists	Re-request a fresh sentinel (wins the race), release old one; fall back to video on failure

  document.addEventListener('visibilitychange', function () {
    if (document.visibilityState !== 'visible') return;
    if (noSleepVideo) {
      if (noSleepVideo.paused) { noSleepVideo.play().catch(function () {}); }
    } else if (!wakeLockSentinel) {
      requestWakeLock();
    } else {
      navigator.wakeLock.request('screen').then(function (newSentinel) {
        try { wakeLockSentinel.release(); } catch (e) {}
        wakeLockSentinel = newSentinel;
        newSentinel.addEventListener('release', function () { wakeLockSentinel = null; });
      }).catch(function () { wakeLockSentinel = null; startNoSleepVideo(); });
    }
  });

• CHANGELOG.md — v4.6.0 entry.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Fire TV (Silk Browser) Disable screen saver from appearing while not in full screen video</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Fire TV (Silk Browser) Disable screen saver from appearing while not in full screen video #99

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