Bidirectional progress sync, reliable background history, MB-accurate download ring

- Bidirectional progress sync: server's `lastUpdate` now parsed correctly; pull
  timer (60s) + scenePhase hook reconcile against local state. Server-newer
  while paused/playing stashes a `pendingServerProgress` and surfaces a prompt
  on next Play; server-older triggers an immediate push.
- History: lockscreen/Control-Center skip & scrub now route through AppState
  via `onRemoteSkip`/`onRemoteSeek` callbacks (previously bypassed history).
  `AppState.skip(by:)` itself now records the pre-skip position.
- Chapter detection moved to the AVPlayer periodic time observer — fires
  reliably while the app is backgrounded or the device is locked, where the
  5s runloop Timer can be throttled.
- Always fetch item detail when online (even for downloaded items) so
  `item.chapters` is populated and history entries get chapter titles.
- DownloadManager: per-track byte-fraction progress, so single-track 1+GB
  audiobooks' ring grows smoothly instead of staying at 0% until done.
- PlayerBar: extracted ScrubberView into its own struct so per-second time
  updates no longer re-render the parent (fixes iOS history-popup flicker).
- App icon: re-embedded sRGB profile in marketing icon; bumped version 2.0
  to 2.1.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ABS Client/Audiobookshelf swift/Services/PlayerEngine.swift

@@ -33,6 +33,17 @@ final class PlayerEngine {
     /// Pausiert mit der Wiedergabe; bei `.endOfBook`/`.endOfChapter` rate-skaliert aus der Restspielzeit.
     var sleepRemainingSeconds: Double = 0
     var chapters: [Chapter] = []
+    /// Set by AppState. Fired when a remote/system control (lockscreen, Control
+    /// Center, headphones) triggers a skip, so AppState can record history and
+    /// run its own seek path instead of bypassing it.
+    var onRemoteSkip: ((Double) -> Void)?
+    /// Set by AppState. Fired when a remote control changes playback position.
+    var onRemoteSeek: ((Double) -> Void)?
+    /// Set by AppState. Fired by the AVPlayer periodic time observer whenever
+    /// playback crosses into a new chapter — works reliably in background and
+    /// with the device locked, unlike a runloop-scheduled Timer.
+    var onChapterChanged: ((Chapter) -> Void)?
+    private var lastObservedChapterId: Int?
 
     var currentChapter: Chapter? {
         chapters.last { $0.start <= absoluteCurrentTime }
@@ -125,6 +136,9 @@ final class PlayerEngine {
         }
 
         self.chapters = item.chapters
+        // Reset chapter tracking — first observation after load is "initial",
+        // not a transition.
+        lastObservedChapterId = nil
         currentTitle = item.title
         currentAuthor = item.author
         currentCoverURL = client.coverURL(itemId: item.id)
@@ -251,6 +265,19 @@ final class PlayerEngine {
         if wasPlaying != isPlaying { updateNowPlayingInfo() }
         updateEndOfBookSleep()
         updateEndOfChapterSleep()
+        detectChapterTransition()
+    }
+
+    private func detectChapterTransition() {
+        let currentId = currentChapter?.id
+        guard currentId != lastObservedChapterId else { return }
+        let priorId = lastObservedChapterId
+        lastObservedChapterId = currentId
+        // Skip the very first observation after load (priorId == nil) — that's
+        // the initial position, not a real transition. AppState records that
+        // separately in `play(item:)`.
+        guard priorId != nil, let chapter = currentChapter else { return }
+        onChapterChanged?(chapter)
     }
 
     func teardown() {
@@ -275,6 +302,7 @@ final class PlayerEngine {
         errorMessage = nil
         isSeeking = false
         chapters = []
+        lastObservedChapterId = nil
         currentTitle = ""
         currentAuthor = ""
         currentCoverURL = nil
@@ -374,12 +402,24 @@ final class PlayerEngine {
         applyRemoteSkipInterval(seconds: Self.currentSkipSeconds())
         center.skipForwardCommand.addTarget { [weak self] _ in
             let s = Double(Self.currentSkipSeconds())
-            Task { @MainActor in self?.skip(by: s) }
+            Task { @MainActor in
+                if let handler = self?.onRemoteSkip {
+                    handler(s)
+                } else {
+                    self?.skip(by: s)
+                }
+            }
             return .success
         }
         center.skipBackwardCommand.addTarget { [weak self] _ in
             let s = Double(Self.currentSkipSeconds())
-            Task { @MainActor in self?.skip(by: -s) }
+            Task { @MainActor in
+                if let handler = self?.onRemoteSkip {
+                    handler(-s)
+                } else {
+                    self?.skip(by: -s)
+                }
+            }
             return .success
         }
         NotificationCenter.default.addObserver(
@@ -394,7 +434,13 @@ final class PlayerEngine {
                 return .commandFailed
             }
             let target = posEvent.positionTime
-            Task { @MainActor in self?.seekAbsolute(target) }
+            Task { @MainActor in
+                if let handler = self?.onRemoteSeek {
+                    handler(target)
+                } else {
+                    self?.seekAbsolute(target)
+                }
+            }
             return .success
         }
         center.changePlaybackRateCommand.supportedPlaybackRates = [0.75, 1.0, 1.25, 1.5, 1.75, 2.0]