Add support for default email signatures in connected accounts

[mishave]

Hi Twenty team,

I’d like to propose adding per-connected-account email signatures to Twenty.

Twenty already supports sending and receiving email from connected accounts, but there is currently no way to define a default signature for outbound messages. In practice, this can push users outside the CRM to send email from their normal inbox, especially where businesses need branded signatures, disclaimers, contact details, or consistent formatting across customer communication.

I opened a prototype PR here for reference: #20862

The prototype adds:

• a per-connected-account emailSignature field
• a settings UI for editing the signature
• automatic insertion into the email composer
• signature replacement when switching the sender account
• server-side sanitisation before storing signature HTML

I’m opening this discussion because the current gap affects whether teams can reliably use Twenty as their primary place for customer email. I’d appreciate guidance on the preferred product direction for email signatures, including whether they should be configured per connected account, per workspace member, or both.