Add section-level sub-navigation and breadcrumbs to improve usability on new.drupal.org pages

Problem Statement

The navigation on new.drupal.org is visually clean and modern, but it is missing two elements that materially impact usability, especially as the site’s information architecture grows.
1. The site does not display breadcrumbs, which makes it difficult for users to understand where they are within the site hierarchy or how they arrived there.
2. When a user enters a section such as “AI”, there is no section-specific sub-navigation. This works for shallow structures, but it does not scale to more complex groupings of pages. Users cannot easily move laterally between related pages or understand the structure of a topic area.

As more topic areas expand, the absence of sub-navigation becomes a barrier to discoverability and orientation.

Proposed Solution

Look at the existing structure at
https://www.drupal.org/about/starshot/initiatives/ai
This section uses a right-rail navigation that exposes the sub-pages related to the AI initiative. The sub-navigation is persistent across all pages in this cluster, allowing users to move smoothly within the section and maintain an understanding of where they are.

We propose implementing a similar section-level sub-navigation pattern for new.drupal.org, along with breadcrumb support. This would improve orientation, reduce friction when moving between related pages, and support richer information architectures as the site evolves.

Expected Benefits

• Clearer sense of place through breadcrumbs
• Better wayfinding within complex topic areas
• More consistent experience compared to established Drupal.org patterns
• Improved usability for new contributors, evaluators, and stakeholders

Additional Notes

This request is not about redesigning the primary navigation. It is focused on restoring expected secondary navigation patterns that Drupal.org already uses successfully and that users rely on for orientation.