fix: dates follow the UI language, not the browser's

Seven sites formatted with a bare toLocaleString()/toLocaleDateString(), so an
English UI on a Hungarian machine printed Hungarian-shaped dates (and the reverse).
They now go through formatDateTime/formatDate, which take the i18n language.

frontend/src/components/AdminUsers.tsx

@@ -431,7 +431,7 @@ function PendingAccessRowView({
           {row.created_at && (
             <span>
               {t("users.pendingAccess.signedUp", {
-                time: new Date(row.created_at).toLocaleString(),
+                time: formatDateTime(row.created_at),
               })}
             </span>
           )}
@@ -619,7 +619,10 @@ function AdminInvites() {
               inv.invited_at
                 ? "settings.invites.inviteConfirmAgain"
                 : "settings.invites.inviteConfirm",
-              { email: inv.email, time: new Date(inv.invited_at ?? 0).toLocaleString() },
+              {
+                email: inv.email,
+                time: formatDateTime(inv.invited_at ?? new Date(0).toISOString()),
+              },
             )}
           </p>
           <InviteLangPicker initial={lang} onPick={(v) => (lang = v)} />
@@ -718,7 +721,7 @@ function AdminInvites() {
                     hint={
                       i.invited_at
                         ? t("settings.invites.invitedAt", {
-                            time: new Date(i.invited_at).toLocaleString(),
+                            time: formatDateTime(i.invited_at),
                           })
                         : t("settings.invites.inviteHint")
                     }
@@ -916,7 +919,7 @@ function InviteRow({
         {inv.requested_at && (
           <div className="text-2xs text-muted">
             {t("settings.invites.requested", {
-              time: new Date(inv.requested_at).toLocaleString(),
+              time: formatDateTime(inv.requested_at),
             })}
           </div>
         )}