create_campaign_draftCreate Campaign DraftBuild a ready-to-launch ad campaign for a product WITHOUT the user having an account yet. Parses the landing page, generates ad creatives, and returns a single checkout link. Give that link to the user: they sign in there, the campaign moves to their account, they pay, and it starts. Use this after estimate_campaign, once the user agreed to advertise. Do NOT ask them to register first.