Install setupWebmail() now creates /etc/cyberpanel dir if missing,
patches dovecot.conf with master passdb block if absent, and skips
gracefully when already configured. Prevents webmail auth failures
on fresh installs where the directory didn't exist yet.
Also adds cybermail_accounts and cybermail_domains CREATE TABLE
statements to upgrade.py applyLoginSystemMigrations() for the
emailDelivery app on existing installs.
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