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/settings.html

@@ -146,7 +146,7 @@
             <dl class="sp-facts">
               <div><dt>Zone</dt><dd class="sp-mono">Europe/Moscow</dd><dd class="sp-muted">UTC+03:00. Set in <code>.env</code> (<code>TZ</code>); restart to change.</dd></div>
             </dl>
-            <p class="mt-4 sp-muted">Every time the panel shows, and every day it counts - today on Health, the days of the statistics - is this zone's, and so are the stamps of <code>mail.log</code>.</p>
+            <p class="mt-4 sp-muted">Every time the panel shows, and every day it counts - today on Health, the days of the statistics - is this zone's, and so are the stamps of <code>mail.log</code>. One exception: the day a DMARC report covers is the reporter's, in UTC.</p>
           </div>
         </div>
       </div>