fix(sub): drive display remarks from the template and split multi-host subpage links

Unify remark generation around the Remark Template. Display contexts (Clients-page QR/Info modals and the HTML sub info page) now render the template name-only client/identity part instead of a hardcoded fallback; the subscription body keeps the full template on a client first link and name-only thereafter. The default template gains the email token so the client email shows by default again (#5532).

BuildPageData now splits each multi-link entry (one link per host of an inbound) into a separate row, so the sub page no longer collapses several host links onto a single mangled line. QR captions on the Clients QR modal and the sub page reuse the link fragment remark.

frontend/src/pages/clients/ClientQrModal.tsx

@@ -106,7 +106,7 @@ export default function ClientQrModal({
         children: (
           <QrPanel
             value={link}
-            remark={`${client?.email || ''} #${idx + 1}`}
+            remark={parts?.remark || `${client?.email || ''} #${idx + 1}`}
             showQr={!isPostQuantumLink(link)}
           />
         ),