feat(course-page): improve resize handle UI and interaction

Update the resize handler on the test results bar to enhance usability
and visual clarity. Replace previous fixed-height bar with a more
distinct and responsive design using flexbox and group hover styles.
This change improves user feedback during resizing and cleans up the
markup by removing obsolete template lint disabling.

Author: rohitpaulk

app/components/course-page/test-results-bar/index.hbs

@@ -5,15 +5,15 @@
   ...attributes
 >
   {{#if this.isExpanded}}
-    {{! template-lint-disable no-pointer-down-event-binding }}
     <div
-      class="absolute bg-gray-700 hover:bg-gray-500 cursor-ns-resize h-1 rounded-sm top-1 w-12 z-10"
+      class="group/resize-handler h-3 bg-transparent absolute top-0 left-0 right-0 flex items-center justify-center cursor-ns-resize z-10"
       role="button"
       {{on "mousedown" this.startResize}}
       {{on "touchstart" this.startResize}}
       data-test-resize-handler
     >
-      <div class="absolute -top-1.5 left-0 right-0 h-4 bg-transparent"></div>
+      <div class="bg-gray-700 group-hover/resize-handler:bg-gray-500 h-0.5 rounded-sm w-16">
+      </div>
     </div>
   {{/if}}