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/views.py

@@ -36,7 +36,7 @@ def item_list(request):
     category = request.GET.get('category', '')
     sort = request.GET.get('sort', 'fav')
     shelf = request.GET.get('shelf', Item.ACTIVE)
-    if shelf not in (Item.ACTIVE, Item.COMPLETED, Item.ABANDONED):
+    if shelf not in (Item.ACTIVE, Item.COMPLETED, Item.ABANDONED, Item.UNENDING):
         shelf = Item.ACTIVE
 
     items = Item.objects.filter(user=request.user, status=shelf)
@@ -88,7 +88,7 @@ def item_set_status(request, pk):
     if request.method == 'POST':
         item = get_object_or_404(Item, pk=pk, user=request.user)
         new_status = request.POST.get('status')
-        if new_status in (Item.ACTIVE, Item.COMPLETED, Item.ABANDONED):
+        if new_status in (Item.ACTIVE, Item.COMPLETED, Item.ABANDONED, Item.UNENDING):
             item.status = new_status
             item.save(update_fields=['status', 'updated_at'])
     next_url = request.POST.get('next') or reverse('backlogger:list')