Promote Teams and Members to top-level navigation

[ObnoxiousProxy]

• Motivation:
  Teams and Members are high-frequency admin tasks and deserve first-class navigation for discoverability.

• Proposed solution:
  Add Teams and Members entries to the app sidebar (frontend/src/components/layout/app-sidebar.tsx) alongside existing items; keep settings sub-nav (features/settings/components/settings-navigation.tsx) unchanged.

• Additional context:

  • Ensure permission gating matches existing settings access.