Adds SERVERFQDN_IMAP and TB_MAIL_FULLNAME to setup_system.conf.dist.
On each logon the script checks if an IMAP account for DAVTOKEN_USER@TLDOMAIN
already exists in prefs.js; if not it writes the server, identity, and account
entries and registers it with accountmanager. Idempotent — skipped when the
account is already present.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>