Add a maximum width for email address

On large viewports, we don't want the hero content part to
endlessly grow if the user's email address happens to be
ridiculously long. This change limits it to a reasonable size that
maintains readability for the regular content, and truncates the
email address if it is wider than that.

src/client/css/partials/exposureScan.css

@@ -43,6 +43,7 @@
   flex-direction: column;
   align-items: flex-start;
   gap: var(--gap);
+  width: var(--max-width-p);
   max-width: 100%;
 }