Document slug auto-generation for all navigation items

[fern-api]

Summary

The navigation page previously only mentioned slug auto-generation in the context of folders ('Converts filenames to titles and URL slugs'). This PR adds a comprehensive 'Slugs and URL paths' section that documents how Fern auto-generates slugs for all navigation items — sections, pages, folders, tabs, versions, and products.

Changes

• Added a new '## Slugs and URL paths' section with:
  • A table showing slug derivation source for each navigation item type
  • Explanation of slug override (relative to position in hierarchy)
  • Explanation of skip-slug and which items support it
  • Cross-reference to frontmatter slug (absolute override)
• Added a note under 'Add a section' that sections support slug and skip-slug (previously undocumented on this page)
• Updated the folder bullet list to link to the new slug section instead of being the only mention of slug generation
• Updated the page meta description to include 'URL slugs'

Requested by: Fern Support

[github-actions]

📝 [vale] _{reported by reviewdog 🐶}
[FernStyles.Headings] 'Slugs and URL paths' should use sentence-style capitalization.

[github-actions]

🌿 Preview your docs: https://fern-preview-fern-document-slug-generation.docs.buildwithfern.com/learn

Here are the markdown pages you've updated:

• learn/docs/configuration/navigation

[fern-api]

Requested by: devin
Slack thread: View conversation