Add chapters, history, bookmarks, live download progress, and i18n

- Chapter navigation with auto-scroll to current chapter and end-of-chapter sleep timer
- Opt-in listening history (local-only) with XML export and per-item quick menu
- Bookmarks with server sync via Audiobookshelf API
- Live MB counter during downloads via URLSessionDownloadTask delegate
- In-progress downloads shown in "Heruntergeladen" with dimmed cover + ring overlay
- Cover image cache (50 MB memory / 500 MB disk URLCache)
- German/English localization (de.lproj, en.lproj)
- Loading spinner now triggers immediately on view switch instead of waiting for the network

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ABS Client/Audiobookshelf swift/Services/PlayerEngine.swift

@@ -15,6 +15,7 @@ enum SleepTimerMode: Equatable, Hashable {
     case off
     case minutes(Int)
     case endOfBook
+    case endOfChapter
 }
 
 @Observable
@@ -29,8 +30,13 @@ final class PlayerEngine {
 
     var sleepTimer: SleepTimerMode = .off
     /// Verbleibende Wallclock-Sekunden bis der Sleep-Timer auslöst (0 wenn off).
-    /// Pausiert mit der Wiedergabe; bei `.endOfBook` rate-skaliert aus der Restspielzeit.
+    /// Pausiert mit der Wiedergabe; bei `.endOfBook`/`.endOfChapter` rate-skaliert aus der Restspielzeit.
     var sleepRemainingSeconds: Double = 0
+    var chapters: [Chapter] = []
+
+    var currentChapter: Chapter? {
+        chapters.last { $0.start <= absoluteCurrentTime }
+    }
 
     private var player: AVQueuePlayer?
     private var trackDurations: [Double] = []
@@ -118,6 +124,7 @@ final class PlayerEngine {
             }
         }
 
+        self.chapters = item.chapters
         currentTitle = item.title
         currentAuthor = item.author
         currentCoverURL = client.coverURL(itemId: item.id)
@@ -159,8 +166,10 @@ final class PlayerEngine {
     func setRate(_ newRate: Float) {
         rate = newRate
         if isPlaying { player?.rate = newRate }
-        if case .endOfBook = sleepTimer {
-            sleepRemainingSeconds = wallclockRemainingUntilEndOfBook()
+        switch sleepTimer {
+        case .endOfBook: sleepRemainingSeconds = wallclockRemainingUntilEndOfBook()
+        case .endOfChapter: sleepRemainingSeconds = wallclockRemainingUntilEndOfChapter()
+        default: break
         }
         updateNowPlayingInfo()
     }
@@ -241,6 +250,7 @@ final class PlayerEngine {
         isPlaying = player.timeControlStatus == .playing
         if wasPlaying != isPlaying { updateNowPlayingInfo() }
         updateEndOfBookSleep()
+        updateEndOfChapterSleep()
     }
 
     func teardown() {
@@ -264,6 +274,7 @@ final class PlayerEngine {
         itemId = nil
         errorMessage = nil
         isSeeking = false
+        chapters = []
         currentTitle = ""
         currentAuthor = ""
         currentCoverURL = nil
@@ -284,6 +295,8 @@ final class PlayerEngine {
             if isPlaying { startSleepTickTask() }
         case .endOfBook:
             sleepRemainingSeconds = wallclockRemainingUntilEndOfBook()
+        case .endOfChapter:
+            sleepRemainingSeconds = wallclockRemainingUntilEndOfChapter()
         }
     }
 
@@ -322,6 +335,22 @@ final class PlayerEngine {
         return playback / r
     }
 
+    private func updateEndOfChapterSleep() {
+        guard case .endOfChapter = sleepTimer else { return }
+        sleepRemainingSeconds = wallclockRemainingUntilEndOfChapter()
+        if sleepRemainingSeconds <= 0 {
+            sleepTimer = .off
+            pause()
+        }
+    }
+
+    private func wallclockRemainingUntilEndOfChapter() -> Double {
+        let chapterEnd = currentChapter?.end ?? totalDuration
+        let playback = max(0, chapterEnd - absoluteCurrentTime)
+        let r = max(0.1, Double(rate))
+        return playback / r
+    }
+
     // MARK: - Now-playing / remote commands
 
     private func configureRemoteCommandsIfNeeded() {