A series never has a user_watch_progress row of its own, so series items
always rendered Played:false with no UnplayedItemCount — every show looked
unwatched in compat clients' library views, and the IsPlayed browse filter
treated all series as unplayed. Roll episode progress up to series rows in
the browse/search/detail paths, mirroring applySeasonUserData and the
native API's rollup semantics (WatchedCount/UnplayedCount/InProgressCount).
Progress lookups are chunked at 500 ids (per-user stores may be
SQLite-backed) and the rollup is capped at 250 series per page so
max-limit browses of series-only libraries stay bounded.
