design: dmarc-day - the reporter's day named as such; confirm's sign-in state

The owner, 2026-10-17: "Показ времени отчёта по UTC принимаем. Это не
проблема. Пояснения добавь. Все мелочи закрой."

A DMARC report's day stays the reporter's, in UTC - the title and the lists
name it - and the panel now says so: the report's Window shows its
boundaries in this panel's zone with a line under them naming the
reporter's day; Settings' Time zone box and Help (#settings, #dmarc) name
it as the one exception to "every time is this zone's".

confirm-email-signin.html: the confirmation link opened without its
account's session (since the security review of password-reset): what to
do, and a link to sign in.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/assets/panel-redesign/panel/dmarc-report.html

@@ -81,7 +81,7 @@
             <dl class="sp-facts">
               <div><dt>Reporter</dt><dd>Outlook.com</dd></div>
               <div><dt>Report id</dt><dd class="sp-mono sp-small">5f1c9a0e7b2d4e61a3</dd></div>
-              <div><dt>Window</dt><dd>20 Sep 00:00 – 21 Sep 00:00</dd></div>
+              <div><dt>Window</dt><dd>20 Sep 03:00 – 21 Sep 03:00</dd><dd class="sp-muted">The reporter's day, 20 Sep: reports count their days in UTC, and the title and the lists name that day. The times are this panel's zone.</dd></div>
               <div><dt>Received</dt><dd>2026-09-21 04:40</dd></div>
             </dl>
           </div>