Section bundles more hierarchy-focused

[smythp]

Summary

Currently, section bundles (accessed primarily through breadcrumb links) show a list of all content pages under that heading recursively. I propose to render down only to the next level and include section bundles in the generated list, allowing traversal one node at a time.

Basic example

-- Docs
  -- About
    |
    -- history.md
    -- contributing.md
  -- API
    |
    -- reference.md
    -- guide.md

Currently, if you go to the section bundle for docs by clicking the "docs" link in the breadcrumb, the page will show you all four content pages (history, contributing, reference, guide).

What I'm proposing would be to have the docs section bundle show instead About and API. When clicking through on those, you would see the content pages under those. This seems like a more intuitive way to navigate the project.

Background

We recently used Doks in a replatform for the Sigstore docs. (thanks, the theme has been great to work with, and you've been extremely helpful.) I implemented this proposed change for our site (try navigating by breadcrumbs or visiting the docs section bundle. Edit: we removed the "docs" breadcrumb level for backward compatability..

Thanks again, and no worries if you (understandably) like the section bundles the way they are.