feat: ABS full playback on Android — chapters, speed, sleep timer, progress sync

- AbsClient: add session API (startSession, closeSession, getProgress, saveProgress, getItemChapters) and data classes (AbsChapter, AbsAudioTrack, AbsPlaySession, AbsProgress)
- AbsPlayerController (new): standalone ExoPlayer controller for ABS audio; tracks global time across multi-track audiobooks, syncs progress to ABS every 30 s, chapter navigation, speed control, sleep timer
- AbsScreen: book detail screen with cover/meta/progress/chapter list/play button; AbsNowPlayingScreen overlay (progress bar, prev/+30s/play/-30s/next controls, speed picker, sleep timer, chapter list with auto-scroll)
- AppNavigation: create AbsPlayerController, wire up book detail and player overlay, hardware back button handling for all ABS sub-screens
- PrefsStore + SettingsViewModel + SettingsScreen: absChapterTrackMode toggle — progress bar shows current chapter length instead of full book
- README: update ABS section to cover both web and Android features

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

README.md

@@ -50,8 +50,13 @@ Built with Vite + vanilla ES modules (web) and Jetpack Compose + Media3/ExoPlaye
 - Create, edit, delete playlists; add / remove tracks
 
 ### Audiobookshelf Integration
-- **Web:** browse libraries, stream audiobooks, chapter navigation, playback speed, sleep timer, progress sync
-- **Android:** browse libraries and audiobook list (tab hidden until ABS is configured in Settings)
+- Browse libraries and audiobooks on both Web and Android
+- Stream audiobooks with chapter-by-chapter navigation
+- Playback speed control (0.5× – 2.0×)
+- Sleep timer
+- Progress sync — current position saved back to ABS server every 30 s
+- Chapter track mode — progress bar shows current chapter length instead of full book (toggle in Settings)
+- Tab/section hidden until ABS is configured in Settings
 
 ### App — Web PWA
 - Installable on Android / iOS / desktop