Save source descriptions, add "Why it's #N", fix IGDB studio names

Descriptions
- Items keep the source's description (TMDB/TheTVDB overview, IGDB
  summary, Wikipedia intro) in a new items.description column
  (migration 3); editable in the item form
- Deezer/MusicBrainz track counts and album names are now display-only
  hints, not saved as descriptions

Why it's #N
- The owner's note is presented as "Why it's #N" in the editor and the
  public detail view, above an "About" section with the description

IGDB developers
- IGDB credits internal divisions ("Nintendo EAD", "Nintendo EPD
  Production Group No. 8"). A developer whose name shares its first word
  with its parent company is credited to the parent ("Nintendo");
  independently named studios keep their name (Retro Studios, Naughty
  Dog, Landfall Games)
- Fall back to the publisher when IGDB lists no developer

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/store/store.go

@@ -111,6 +111,8 @@ CREATE INDEX items_list_rank ON items(list_id, rank);
 `,
 	// Per-list artwork shape; '' uses the category's default.
 	`ALTER TABLE lists ADD COLUMN art TEXT NOT NULL DEFAULT '';`,
+	// The source's description of the item (TMDB overview, IGDB summary…).
+	`ALTER TABLE items ADD COLUMN description TEXT NOT NULL DEFAULT '';`,
 }
 
 func (s *Store) migrate(ctx context.Context) error {