fix(dashboard): fix widget nav button on iOS; lift header above backdrop-filter

widgetHeader replaces <a href> with <button type="button"> so iOS Safari
does not intercept the touch event before the JS click handler fires.
widget__header gets position: relative; z-index: 2 to appear above the
backdrop-filter ::after pseudo-element stacking context.

public/pages/dashboard.js

@@ -119,9 +119,9 @@ function widgetHeader(icon, title, count, linkHref, linkLabel) {
         ${title}
         ${badge}
       </span>
-      <a href="${linkHref}" data-route="${linkHref}" class="widget__link">
+      <button type="button" data-route="${linkHref}" class="widget__link">
         ${linkLabel}
-      </a>
+      </button>
     </div>
   `;
 }