fix: patch null crash, NaN guard, buffer seek, ad skip, premiere detection
- video undefined after re-render now returns early instead of throwing every 500ms
- guard against NaN/0 duration before computing scaleX
- buffer bar now tracks the buffered range containing currentTime, not always end(0)
- skip interval update during ads (.ad-showing)
- replace ytp-live-badge check with duration === Infinity for accurate premiere support
- call main() on script load to catch direct /watch URL visits
- fix observe() ignoring its dom parameter
- rename internal → interval; fix intitailized/cancaled typos