EmailDraftSettings

Serialised state of the Create Email dialogue at autosave time.

Adds the fields the schedule path doesn't need: subject, html, attachments, email_template_id, the content-sharing scope, the mass-mail toggle, and the "additional linked items" surface unique to standard mail.

Backing column: email.draft_settings (JSONB, added in v640_01). Written by saveEmailDraft; read by EmailEntity.draft_settings when the FE re-opens an existing draft in Create Email.