Audiobookshelf-style exports join genres into one comma-string
(["Epic, Action & Adventure, Military, Sword & Sorcery"]). The
smart-genre picker already split candidates for the genre column,
but the tags assembly used the raw unsplit array — so the whole
string landed as ONE element of media_items.tags and rendered as a
single tag everywhere.
Use pickSmartGenre's split candidates for tags too, exactly as the
function's own comment documents ('split parts included stay in
tags'). Commas inside a single subject heading remain legal within
one tag (EPUB dc:subject path unchanged).