As a page navigator, I want group sub-pages to be collapsed, so that I can navigate better

### 📝 Description

Having every subpage visible for groups could potentially add clutter. By only having them show once a user visits that group, this could be eliminated.

### ✅ Acceptance Criteria

- [ ] Collapse group sub-pages until the user visits the root group page

### 💡 Additional context

_No response_

No files or tests are named in the issue. Start by locating the page-navigation entry point that renders group sub-pages, then trace how visits to a root group page are detected. Done means group sub-pages remain collapsed until that visit and navigation is less cluttered.

Written by the indexing model from the issue text.