Harden Disney+ time fallback against <video> element recreation

When the control overlay (and its live time readout) is briefly absent,
the old fallback recomputed the timeline from the raw blob-relative
video.currentTime via a cached scale/start. Disney recreates the <video>
element on some play/pause transitions, which resets currentTime, so that
math produced a wildly wrong time ("loses the time" after a pause).

The native clock advances 1:1 with real playback, so instead anchor the
last live UI position to video.currentTime and extrapolate by the elapsed
native delta. If the delta is negative or implausibly large (element
recreated / seek), freeze at the last known position rather than emitting
a garbage time.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

scripts/test-content-video-finder.cjs

@@ -94,6 +94,8 @@ function loadTimelineFns(hostname, document = makeDocument()) {
     'let lastKnownDisneyPlusDuration = 0;',
     'let lastKnownDisneyPlusScale = 1;',
     'let lastKnownDisneyPlusStart = 0;',
+    'let lastDisneyPlusUiCurrent = null;',
+    'let lastDisneyPlusNativeAtUi = null;',
     extractFunction('scanShadowDom', source),
     extractFunction('querySelectorAllShadow', source),
     extractFunction('hostMatchesUrl', source),