Service now delegates to window.Manager, systray.Manager, and menu.Manager
instead of directly using Wails types. WSEventManager accepts EventSource
interface instead of calling application.Get() directly.
AttachWindowListeners now accepts window.PlatformWindow.
Removes migrated files: window.go, window_state.go, layout.go, tray.go, menu.go.
Tests rewritten against mock platform implementations.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
