Feature request: have the possibility of displaying challenge categories collapsed, and the challenges themselves as a list so that they take up less space

Feature request: have the possibility of displaying challenge categories collapsed, and then, when a category is expanded, load the challenges themselves as a list so that they take up less space.

Why is this useful? If there would be 10 categories with 30 challenges each, the challenges page would load too slowly, and the page itself would be "lengthy".

Start at the challenges page and trace how categories and their challenges are rendered and loaded. Define the collapsed-category and expanded-list behavior, then verify that the page uses less space and avoids loading every challenge before a category is opened.

Written by the indexing model from the issue text.