The Email Server builtin extension's backend package was present on disk (and
exercised by the green test suite) but never tracked. Adds it alongside the
already-tracked serverkit-gpu / serverkit-gui backend plugins: the Flask
blueprint (email.py) plus the Postfix/Dovecot/DKIM/SpamAssassin/Roundcube
service modules. __pycache__ stays gitignored.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>