Modernize the iOS App UI

This proposal aims to modernize the OneBusAway iOS app by replacing the current tab bar navigation with a SwiftUI-based, Apple Maps–style sheet interface. It involves removing the legacy navigation system and introducing a new SwiftUI root view with a persistent bottom sheet that unifies key features, including search, nearby stops, arrivals, bookmarks, recent stops, and settings. The project will also ensure full VoiceOver accessibility support and establish a scalable SwiftUI foundation, enabling future features and incremental migration without revisiting the navigation architecture.