AddDomainSheet now opens with a Seite / E-Mail segmented control.
Web keeps the existing flow (label, placeholder, favicon preview,
domain normalization). Mail switches to a free-form pattern input
(address / domain / display-name — user types what they see in
their inbox) with a mail-icon preview after the field is filled.
addDomain(pattern, kind) now sends { pattern, kind: 'web' | 'mail' }
and the server decides the concrete type. Type field flows through
the CustomDomain type so DomainGrid tiles render the mail-outline
icon for mail entries instead of the favicon fallback.
i18n: blocker.type_web / type_mail / add_web_* / add_mail_* across
de/en/fr with %{var} placeholders per repo convention.
