Return the user's ongoing (draft) chats, grouped by category.

A chat is included here when its latest report is in draft status, or when no report has been generated yet. Because draft reports do not yet have a domain_name in the DB, every entry currently lands under the standard key. Additional category keys will start appearing on this response once drafts begin carrying a domain.

Within each group, chats are ordered by updated_at descending (most-recent first).

Authentication Required: Yes (JWT token)