Fix unending: shelf status, not category

Unending belongs in STATUS_CHOICES alongside completed/abandoned.
Adds an Unending shelf tab and an ∞ button on active game cards.
Reverts the incorrect category addition from the previous commit.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backlogger/models.py

@@ -6,23 +6,23 @@ class Item(models.Model):
     GAMES = 'games'
     BOOKS = 'books'
     FILMS = 'films'
-    UNENDING = 'unending'
     OTHER = 'other'
     CATEGORY_CHOICES = [
         (GAMES, 'Games'),
         (BOOKS, 'Books'),
         (FILMS, 'Films'),
-        (UNENDING, 'Unending'),
         (OTHER, 'Other'),
     ]
 
     ACTIVE = 'active'
     COMPLETED = 'completed'
     ABANDONED = 'abandoned'
+    UNENDING = 'unending'
     STATUS_CHOICES = [
         (ACTIVE, 'Active'),
         (COMPLETED, 'Completed'),
         (ABANDONED, 'Abandoned'),
+        (UNENDING, 'Unending'),
     ]
 
     user = models.ForeignKey(User, on_delete=models.CASCADE, related_name='items', null=True)