Personal ordered lists of Plex items, kept in Siftlode's own DB (works for users
without a Plex account, like watch-state) — the "your own lists" counterpart to
shared collections. Plex-direction sync is a later phase (plex_rating_key
reserved).
Backend: migration 0048 (plex_playlists + plex_playlist_items with position),
PlexPlaylist/PlexPlaylistItem models, and per-user CRUD endpoints under
/api/plex/playlists (list [+?contains for the add dialog], create [seeded],
detail [ordered cards], rename, delete, add/remove item, reorder). _leaf_card
handles the movie/episode mix. Frontend: "Add to playlist" dialog from the movie
info page (all users), a Playlists section in PlexSidebar (list + create),
PlexPlaylistView (reorder up/down, remove, rename, delete, Play all), and
PlexPlayer gained an optional `queue` so play-through follows the list order
(prev/next + auto-advance). i18n en/hu/de. Verified end-to-end on localdev
(backend CRUD + the create→add→view→play-through UI flow).
