Navigation and URL model simplification

[KOTungseth]

Description

Audit current path prefixes and navigation patterns.

• Reduce complexity where possible and clearly document rules.
• Enable redirects based on path prefixes.

Acceptance criteria

• Writers can reliably edit navigation and configure redirects without engineering support.
• Path prefixes are documented, consistent, and simplified where possible.
• Contributors can add/update navigation.yml entries across repos without engineering help.
• Redirects based on path prefixes are supported and documented.