When auto-advancing through a queue or playlist — or stepping with
next/prev — the next video previously jumped to its saved resume
timestamp. A freshly selected track now starts at the beginning, or at
the A marker when an A-B loop is set for it. Resuming still applies when
you reopen a single video directly.
A-B markers set while playing from a playlist are now stored on that
playlist's own copy of the video (entry.ab), so each playlist keeps its
own loop and the markers sync to the database alongside the playlist.
Non-playlist playback keeps using the global per-video marker map.
Bumps service worker to v1.0.3 to bust the client cache.
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