What changed (mutual exclusion):
- Enter native fullscreen → tab-fill overlay suspends (yt-tabfs-realfs class, CSS
scoped :not(.yt-tabfs-realfs)), restores on exit.
- Toggle tab-fs on while in native fullscreen → exits native fullscreen first.
- Both directions nudge YouTube to re-lay-out.
- Verified: no regression (tab-fill still fills + restores), both dists carry the
fix.

Bug fixes:
• Turning tab-fullscreen off now restores the video correctly —
it no longer stays enlarged and stuck in the top-left corner.
• The control bar now spans the full width of the screen when
tab-fullscreen is on.
• Fixed the Alt+T shortcut occasionally double-firing and
cancelling itself.
• More reliable on/off state syncing.