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/Audiobookshelf_swiftApp.swift

@@ -1,11 +1,19 @@
 import SwiftUI
 #if os(iOS)
 import AVFAudio
+import UIKit
 #endif
 
 @main
 struct Audiobookshelf_swiftApp: App {
     @State private var appState = AppState()
+    #if os(iOS)
+    /// Bridges the UIKit-only `handleEventsForBackgroundURLSession` callback
+    /// (used by iOS to wake the app when a background download completes)
+    /// into the SwiftUI lifecycle. Without this, in-flight downloads can't
+    /// notify the app of completion after a swipe-away.
+    @UIApplicationDelegateAdaptor(BackgroundDownloadAppDelegate.self) private var appDelegate
+    #endif
 
     init() {
         configureImageCache()
@@ -54,3 +62,20 @@ struct Audiobookshelf_swiftApp: App {
     }
     #endif
 }
+
+#if os(iOS)
+/// Receives the system's background URLSession completion callback and routes
+/// the handler to whichever `DownloadManager` is currently active. We can't
+/// reach the SwiftUI-owned `AppState` from here directly, so the handler is
+/// stashed on `DownloadManager.pendingBackgroundCompletion` and consumed when
+/// `urlSessionDidFinishEvents(forBackgroundURLSession:)` fires.
+final class BackgroundDownloadAppDelegate: NSObject, UIApplicationDelegate {
+    func application(
+        _ application: UIApplication,
+        handleEventsForBackgroundURLSession identifier: String,
+        completionHandler: @escaping () -> Void
+    ) {
+        DownloadManager.pendingBackgroundCompletion = completionHandler
+    }
+}
+#endif