Add hashtag helper bar to Explore tab and refactor ID

- Add `#videoListTags` container to `views/explore.html` to support the hashtag helper bar in the Explore view.
- Rename `#recentVideoTags` to `#videoListTags` in `views/most-recent-videos.html` for consistency across views.
- Update `js/ui/videoListViewController.js` and `js/app.js` to reference the new generic `#videoListTags` ID.
- Update `tests/ui/video-list-view-popular-tags.test.mjs` to reflect the ID change.

This enables the hashtag aggregation and interaction features (filtering, muting, following) on the Explore tab, reusing the existing `VideoListView` logic.

views/explore.html

@@ -25,6 +25,7 @@
       </svg>
     </button>
   </div>
+  <div id="videoListTags" class="mb-4" hidden></div>
   <div id="videoList" class="bv-grid-video">
     <div class="sidebar-loading-wrapper" role="status" aria-live="polite">
       <div class="sidebar-loading-indicator">