- Add UserDefaults extension for KVO-compatible updateChannel property
- Fix HTTPField.Name API changes in AuthenticationMiddleware
- Add @preconcurrency annotations to SparkleUpdaterManager protocols
- Wrap KVO observer callback in Task { @MainActor } to fix concurrency warning
- Update deinit to avoid accessing MainActor-isolated properties
These changes address Swift 6 concurrency strictness and API changes
introduced in Hummingbird 2.14.1.
Replace deprecated showSettingsWindow: selector with NSApp.openSettings() to properly show the Settings window when clicking "Settings..." in the menu bar. This aligns with the correct SwiftUI pattern used in VibeMeter.