Handles the rendered-document webhook from either PDF provider (PDFMonkey or caresquare-pdf-generation) and records the result on the remittance.

Uses the async Supabase client so a batch of deliveries does not block the worker's event loop. The synchronous client would stall every other request on this worker for the duration of each update, which is noticeable when a large ABA run delivers hundreds of webhooks at once.