Generate a DUA (Declaração Única Automóvel) PDF document.

Fills a DUA PDF template with buyer/seller data, vehicle info, banking details, and current date. Creates a Registos record and uploads the filled PDF to S3.

PARTIAL GENERATION: all four ids are OPTIONAL. The user fills whatever part of the dossier they have and the rest of the official form is left blank, exactly as a human hand-filling it would. An id that IS supplied must still resolve inside the caller's company — an unresolvable id is a 400, never a blank field.

Body (all optional): sujeito_ativo_id: int — Buyer client ID sujeito_passivo_id: int — Seller client ID vehicle_id: int — Vehicle ID restituicao_pv_id: int — PV ID for banking/restitution data

Returns: {status, registo_id, document_id, s3_url, pdf_url, is_partial, message}