Fetches user_full_name (givenname + sn) and user_email from FreeIPA via
ipalib and writes them into the Thunderbird IMAP account prefs. Adds
ipalib availability check to logon_script.sh. Drops TB_MAIL_FULLNAME
config variable.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>