Add completed/abandoned shelves with status transitions

Items can be moved to Completed or Abandoned via card buttons.
Only active items appear in the default/category tabs; completed and
abandoned items are visible only in their respective shelf tabs.
Restore button moves items back to active.

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

backlogger/urls.py

@@ -7,6 +7,7 @@ urlpatterns = [
     path('add/', views.item_add, name='add'),
     path('<int:pk>/edit/', views.item_edit, name='edit'),
     path('<int:pk>/delete/', views.item_delete, name='delete'),
+    path('<int:pk>/status/', views.item_set_status, name='set_status'),
     path('steam/login/', views.steam_login, name='steam_login'),
     path('steam/callback/', views.steam_callback, name='steam_callback'),
     path('steam/import/', views.steam_import, name='steam_import'),