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.xcodeproj/project.pbxproj

@@ -287,7 +287,7 @@
 					"@executable_path/Frameworks",
 				);
 				MACOSX_DEPLOYMENT_TARGET = 26.0;
-				MARKETING_VERSION = 2.0;
+				MARKETING_VERSION = 2.1;
 				PRODUCT_BUNDLE_IDENTIFIER = "com.local.ABS-Client";
 				PRODUCT_NAME = "ABS Client";
 				REGISTER_APP_GROUPS = YES;
@@ -341,7 +341,7 @@
 					"@executable_path/Frameworks",
 				);
 				MACOSX_DEPLOYMENT_TARGET = 26.0;
-				MARKETING_VERSION = 2.0;
+				MARKETING_VERSION = 2.1;
 				PRODUCT_BUNDLE_IDENTIFIER = "com.local.ABS-Client";
 				PRODUCT_NAME = "ABS Client";
 				REGISTER_APP_GROUPS = YES;