Approach

Introduce NavigatorActivity shell activity that hosts fragments via FragmentContainerView. All screens that previously had their own activity are migrated to fragments and pushed through Navigator. NavigatorScreen sealed class represents each destination.

DrawerActivity launches NavigatorActivity with the target NavigatorScreen as a parcelable extra, keeping the call site clean with no per-screen logic.

Why FileDisplayActivity is not used?

Other activities like SettingsActivity and various non-drawer activities also trigger drawer navigation items. Wiring Navigator into FDA from the start would require every caller to hold a reference to FDA or route through it, which is not possible without a larger refactor. e.g. Navigating from CommunityActivity to some other activity.

This way any activity can launch NavigatorActivity via a simple Intent, no FDA dependency required. Once all navigation is consolidated into NavigatorActivity we can remove it and just use FDA