Fetch checklists

Returns the checklists visible to the authenticated user. Pass an event_id to limit results to checklists attached to a specific event (booking or proposal); omit it to get every checklist the user can see across the franchise (event checklists, the user's personal staff checklist, and any franchise-level checklists).

Visibility is determined automatically based on the authenticated user's role: admins see every checklist; staff see their personal checklist plus event checklists they're assigned to or that allow staff view; customers see their event checklists where customer view is allowed.

Each checklist includes a complete_count (number of checked items) and count (total items) to support progress displays without a separate request.