Add navigation overview page

[fern-api]

Summary

Adds a Navigation overview page at the top of the Configuration > Navigation subsection, introducing the levers that shape a site's information architecture before readers dive into per-lever detail pages.

The page covers:

• The five structural levers (products, versions, tabs, sections, pages) and how they nest, with a two-file YAML example showing products in docs.yml delegating tabs/navigation to a product YML
• Which file holds the navigation key depending on whether products/versions are in use
• Sidebar entry types (page, folder, section, api, changelog, link) as a table linking to each reference
• Per-entry controls (icon, slug/skip-slug, hidden, availability, collapsed, viewers)
• A pointer to site-level settings for navbar/logo/footer, which are not navigation entries

Also adds a card to the existing Configuration overview page so the new page is reachable from that hub.

Requested by: Fern Support

[github-actions]

🌿 Preview your docs: https://fern-preview-fern-navigation-overview.docs.buildwithfern.com/learn

Here are the markdown pages you've updated:

• learn/docs/configuration/page-level-settings
• learn/docs/configuration/navigation-overview
• learn/docs/configuration/overview
• learn/docs/configuration/site-level-settings
• learn/docs/configuration/tabs

[fern-api]

Requested by: devin.logan
Slack thread: View conversation