Fix undefined IGDB_ARTWORK_TYPE_HERO NameError in key-art classification

IGDB_ARTWORK_TYPE_HERO was never defined; the only artwork-type constant
in this module is IGDB_ARTWORK_TYPE_KEY_ART, which this comparison was
clearly meant to use. Left as-is this crashes with a NameError the
first time list artwork classification runs against IGDB's artworks
endpoint.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: dannyvfilms

src/lists/models.py

@@ -973,7 +973,7 @@ def _get_igdb_carousel_media(self, media_id):
                             artwork_types[artwork["id"]] = artwork["artwork_type"]
 
                 for artwork_id, image_id in artwork_image_ids.items():
-                    if artwork_types.get(artwork_id) == IGDB_ARTWORK_TYPE_HERO:
+                    if artwork_types.get(artwork_id) == IGDB_ARTWORK_TYPE_KEY_ART:
                         key_art_image_ids.append(image_id)
                     else:
                         other_artwork_image_ids.append(image_id)