Fix tests for renamed fixtures and new stacked notifications

Clear assignee's existing notifications in setup since Notifier now
uses create_or_find_by instead of create, and reload the association
to avoid caching after destroy_all.

Update fixture references after rebase: use `logo_assignment_kevin`
as base notification and `logo_mentioned_david` for mention tests.
Update source to `logo_published` in tests that need generic card events.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

test/integration/notifications_test.rb

@@ -7,6 +7,7 @@ class NotificationDeliveryTest < ActiveSupport::TestCase
     @card = cards(:logo)
 
     @card.assignments.destroy_all
+    @assignee.notifications.destroy_all
 
     stub_web_push_pool
 
@@ -55,7 +56,7 @@ class NotificationDeliveryTest < ActiveSupport::TestCase
       end
     end
 
-    notification = @assignee.notifications.last
+    notification = @assignee.notifications.reload.last
     assert_not_nil notification, "Notification should be created for assignee"
 
     bundle = @assignee.notification_bundles.pending.last