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/providers/wikipedia.go

@@ -99,7 +99,7 @@ func (w *wikipedia) search(ctx context.Context, query string) ([]Result, error)
 			Year:        yearOf(p.Description),
 			ImageURL:    img,
 			ExternalURL: p.FullURL,
-			Overview:    truncate(p.Extract, 600),
+			Overview:    truncate(p.Extract, maxDescription),
 		})
 	}
 	return out, nil