Drop question-report entirely, obfuscate the mailto link instead

The report button logged to an event stream nothing ever read - no
notification, no dashboard, just a durable no-op. A browser back
button already covers "this page wasn't helpful" better than a button
that silently does nothing visible to anyone but the visitor who
clicked it.

The mailto address is now assembled from data-user/data-domain on a
real mouse event instead of baked into the server-rendered href -
keeps a plain mailto: string (what bulk scrapers regex HTML for) out
of what a generic bot crawl sees, without hiding the contact option
from an actual visitor.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

style/main.css

@@ -254,25 +254,6 @@ main.not-found {
   color: var(--accent);
 }
 
-.question-report {
-  font: inherit;
-  color: var(--ink-dim);
-  background: none;
-  border: none;
-  padding: 0;
-  text-decoration: underline;
-  cursor: pointer;
-}
-
-.question-report:hover {
-  color: var(--accent);
-}
-
-.question-report:disabled {
-  opacity: 0.5;
-  cursor: wait;
-}
-
 .alt-card {
   background: var(--paper-raised);
   border: 1px solid var(--line);