Marks a classic proposal sent, saves its PDF to the deal's documents, and emails the PDF to the deal's contact when they have an email address and have not opted out of email. The proposal is marked sent either way, and message says whether the email went out.

To send the homeowner a link where they can view and accept the proposal instead, use POST /proposals/{id}/send_link. The token's role must be allowed to prepare estimates, and must either have access to all records or be the sales rep assigned to the deal.