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>
   `;
 }

public/styles/dashboard.css

@@ -187,6 +187,8 @@
   align-items: center;
   justify-content: space-between;
   padding: var(--space-3) var(--space-4) var(--space-2);
+  position: relative;
+  z-index: 2;
 }
 
 .widget__title {