Mirrors the azos-core change: features/mail/default.nix now just sets
accounts.email.accounts (the three real addresses, with the existing
default_account_params/default_gmail_params convenience merging kept
here since it's personal boilerplate, not mechanism) and
azos.mail.presenceCheckCommand, wired to azos-card-present only when
azos.encryption.yubikey.enable is true.
aner
ac6c15f931