Record live monitor.php cron config in HOSTING.md and close todo 05.
Move optional */5 heartbeat task to todo/13.
Co-authored-by: Cursor <cursoragent@cursor.com>
Add mail.php with STARTTLS sending, test scripts, server.env split from
local .env, admin@ postbox docs, DKIM DNS support-ticket notes, and todo 11
for boka relay.
Co-authored-by: Cursor <cursoragent@cursor.com>