Workspace-level email sync policy: admin defaults + "contact-associated only" retention

[gpearreomne]

Problem.
Email sync settings (visibility, contact auto-creation, group/non-professional exclusions) are per mailbox, set by each user. Admins can't set defaults or enforce a policy. Twenty also imports and stores every message in the synced folders, whether or not it involves a CRM contact. In practice:

• Personal and unrelated mail ends up in the database (bank alerts, newsletters, an earlier job's correspondence). It's readable through the API and MCP even though it never appears on a record.
• A new user's first import, with auto-creation on, can create hundreds of junk People and Companies from their history before anyone can change the setting. We had to clean up 861 People and 48 Companies from one user's calendar.
• Choosing Inbox + Sent doesn't filter much, since almost everything lands in the Inbox.

Proposal.

1. Workspace sync policy in admin settings. Defaults for visibility, contact auto-creation and exclusions, applied to newly connected accounts, with an option to lock them so users can't change them.
2. "Contact-associated only" retention mode. After import and participant matching, keep threads only if at least one participant is linked to a Person, and discard the rest after a configurable grace period, so a contact created shortly afterward can still pick up its history. This allows full-content sharing for CRM email with no exposure for everything else.

Why. CRM email should be shared by default and personal email should never be stored. Right now, self-hosters have to build external database triggers and purge jobs to get there.

[BOHEUS]

@neo773