Encode empty checkboxlist arrays as an empty scalar so multipart requests
include the field. On delete, PUT only coupon and tag fields to Mailwizz
after merging the tag CSV from getSubscriber.
Made-with: Cursor
Run CleanupSubscriberIntegrationsService before delete: remove coupon code
in Weeztix via list+DELETE API; update Mailwizz contact to strip configured
source tag from the tag field and clear the mapped coupon field.
Extract MailwizzCheckboxlistTags and MailwizzSubscriberFormPayload for
shared sync/cleanup behaviour. Add WeeztixService list and delete helpers.
Integration failures are logged only; local delete always proceeds.
Feature tests cover Mailwizz strip+clear and Weeztix delete paths.
Made-with: Cursor
