Users can now register as name@guschin.info or name@xmpp.guschin.info.
Added Let's Encrypt cert mounting and install for guschin.info domain.
Refactored entrypoint cert install into reusable function.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
VirtualHost changed from "guschin.info" to "xmpp.guschin.info" to match
the Let's Encrypt certificate. Moved certificates directive before
VirtualHost block. Removed misplaced default_realm and global ssl block.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>