Delete contact

Permanently delete a contact and its communication channels. Implements right-to-erasure obligations under GDPR Art. 17, Ley 19.628 (Chile) Art. 12, CCPA § 1798.105, and LGPD Art. 18.VI. The contact, its channels and any associated agent flow sessions are removed. Conversation threads, message history and broadcast delivery logs are kept and no longer reference the deleted contact.