Enhance download notifications and settings; add support for live activities

- Updated notification body to use proper German quotation marks for download failure alerts.
- Refactored audio interruption handling in PlayerEngine to utilize MainActor.assumeIsolated for better performance.
- Introduced nonisolated properties for support and downloads directories in ProgressSyncManager.
- Improved FullHistoryView and MainView with additional toolbar items and alerts for download failures.
- Added new toggles in SettingsView for parallel downloads and mobile data usage.
- Created new color assets for the DownloadWidgetExtension and updated widget appearance.
- Implemented Info.plist for DownloadWidgetExtension to support widget functionality.
- Enabled live activities support in iOS Info.plist.

ABS Client/Audiobookshelf swift/Services/PlayerEngine.swift

@@ -519,7 +519,9 @@ final class PlayerEngine {
             object: AVAudioSession.sharedInstance(),
             queue: .main
         ) { [weak self] notification in
-            Task { @MainActor [weak self] in
+            // Already on .main queue — assumeIsolated hops to MainActor without
+            // a Task, which would otherwise capture Notification (non-Sendable).
+            MainActor.assumeIsolated {
                 self?.handleAudioInterruption(notification: notification)
             }
         }
@@ -529,7 +531,7 @@ final class PlayerEngine {
             object: AVAudioSession.sharedInstance(),
             queue: .main
         ) { [weak self] notification in
-            Task { @MainActor [weak self] in
+            MainActor.assumeIsolated {
                 self?.handleRouteChange(notification: notification)
             }
         }