media: webtoon metadata (English title, artist, synopsis, years, adaptation) and stored covers with a cover grid

scripts/media-import.ts

@@ -14,7 +14,7 @@
  *   title, creator | author | host | channel, platform, genre, status, progress | episode | chapter,
  *   total | total_episodes, series_status (ongoing|completed, webtoons), form (channel|video|playlist,
  *   videos), url, cover_url (https), rating (0.5–5), who (stan|juhee|both), started, finished
- *   (YYYY-MM-DD), notes.
+ *   (YYYY-MM-DD), notes, title_en, artist, synopsis, year_start, year_end, adaptation, source_ref.
  * Statuses: webtoons reading|completed|on_hold|dropped|plan; podcasts listening|caught_up|paused|
  *   dropped|plan; videos watching|following|watched|dropped|plan ("plan to read" etc. map to plan).
  */