What problems was I solving

The navigation items documentation was stale after the introduction of the navigationGate property for tenant cohort-based visibility. The code snippet was missing the required title field and omitted documentation for the new navigationGate property, which could cause TypeScript compilation errors for developers following the example.

What user-facing changes did I ship

None - this is a documentation-only change that corrects developer guidance.

How I implemented it

Updated the Navigation and Breadcrumbs section in architect/management-ui/app/AGENTS.md to: (1) correctly document that all navigation items require icon, url, and title fields; (2) add explanation of the navigationGate property for tenant cohort-based visibility (values: 'legacy-pages' or 'field-agent'); (3) update the code example to include all required fields and demonstrate the navigationGate property.

Description for the changelog

Updated developer documentation for the management UI navigation system to reflect the correct structure (including all required fields) and document the new tenant cohort-based visibility control via the navigationGate property. This prevents TypeScript compilation errors for developers following the navigation item creation pattern.