API v2: email a sale document to the customer and download its PDF

API v2 has no endpoint to email a sale document (invoice, credit note) to the customer, and none to retrieve its PDF. Templates is GET only.

Request:
- An endpoint such as POST /sale/email (TaskID, document type, template, optional recipients) that sends the document exactly like the Email button in the UI.
- An endpoint to download the rendered PDF of a sale document.

Use case: our automations create and check documents via the API but cannot deliver them. Automation Workflows send on authorisation, before an external system can verify the document.