Append the sender's email signature to outbound emails

Scenario When a user sends an email from Twenty through a connected Google account (the record composer, the AI send-email tool, or the workflow *Send Email* action), the email arrives without their signature. This is because a Gmail signature is applied only by the Gmail web/mobile compose UI — the Gmail API (users.messages.send) does not append it — and Twenty's outbound path has no signature handling. So every email sent from Twenty goes out unsigned, which is a problem for sales/support teams who rely on their work signature (name, title, company, disclaimer) on outbound mail. Proposed solution Read the sender's default signature from the Gmail users.settings.sendAs API and append it to the outgoing message, at the single provider-dispatch point (MessagingMessageOutboundService.sendMessage) so all send paths are covered. • No new OAuth scope — reading sendAs settings is already covered by the gmail.readonly scope connected accounts hold (the existing GoogleEma…