iOS: replace shuffle/repeat with time skip and add chapter navigation to full player

- Leftmost button: 15-second backward skip (gobackward.15)
- Second button: previous chapter navigation (backward.end.fill)
- Center: play/pause (unchanged)
- Fourth button: next chapter navigation (forward.end.fill)
- Rightmost button: 15-second forward skip (goforward.15)
- Added prevChapter tracking in AudioPlayerService
- Added skipToPrevChapter notification support
- Chapter nav buttons disabled when no prev/next available (0.5 opacity)
- Updated load() signature to accept prevChapter parameter
- Auto-next properly tracks prevChapter when advancing chapters

ios/LibNovel/LibNovel/Services/AudioPlayerService.swift

@@ -33,6 +33,7 @@ final class AudioPlayerService: ObservableObject {
 
     @Published var autoNext: Bool = false
     @Published var nextChapter: Int? = nil
+    @Published var prevChapter: Int? = nil
 
     @Published var nextPrefetchStatus: NextPrefetchStatus = .none
     @Published var nextAudioURL: String = ""
@@ -73,7 +74,7 @@ final class AudioPlayerService: ObservableObject {
     /// Load audio for a specific chapter. Triggers TTS generation if not cached.
     func load(slug: String, chapter: Int, chapterTitle: String,
               bookTitle: String, coverURL: String, voice: String, speed: Double,
-              chapters: [ChapterIndexBrief], nextChapter: Int?) {
+              chapters: [ChapterIndexBrief], nextChapter: Int?, prevChapter: Int?) {
         generationTask?.cancel()
         prefetchTask?.cancel()
         stop()
@@ -87,6 +88,7 @@ final class AudioPlayerService: ObservableObject {
         self.speed = speed
         self.chapters = chapters
         self.nextChapter = nextChapter
+        self.prevChapter = prevChapter
         self.nextPrefetchStatus = .none
         self.nextAudioURL = ""
         self.nextPrefetchedChapter = nil
@@ -328,6 +330,7 @@ final class AudioPlayerService: ObservableObject {
 
         let nextTitle = chapters.first(where: { $0.number == next })?.title ?? ""
         let nextNextChapter = chapters.first(where: { $0.number > next })?.number
+        let nextPrevChapter: Int? = chapter  // Current chapter becomes previous for the next one
 
         // If we already prefetched a URL for the next chapter, skip straight to
         // playback and kick off generation in the background for the one after.
@@ -338,6 +341,7 @@ final class AudioPlayerService: ObservableObject {
             chapter = next
             chapterTitle = nextTitle
             nextChapter = nextNextChapter
+            prevChapter = nextPrevChapter
             nextPrefetchStatus = .none
             nextAudioURL = ""
             nextPrefetchedChapter = nil
@@ -360,7 +364,8 @@ final class AudioPlayerService: ObservableObject {
                 voice: voice,
                 speed: speed,
                 chapters: chapters,
-                nextChapter: nextNextChapter
+                nextChapter: nextNextChapter,
+                prevChapter: nextPrevChapter
             )
         }
     }
@@ -462,4 +467,6 @@ enum AudioPlayerStatus: Equatable {
 
 extension Notification.Name {
     static let audioDidFinishChapter = Notification.Name("audioDidFinishChapter")
+    static let skipToNextChapter = Notification.Name("skipToNextChapter")
+    static let skipToPrevChapter = Notification.Name("skipToPrevChapter")
 }

ios/LibNovel/LibNovel/ViewModels/ChapterReaderViewModel.swift

@@ -47,6 +47,7 @@ final class ChapterReaderViewModel: ObservableObject {
             audioPlayer.togglePlayPause()
         } else {
             let nextChapter: Int? = content.next
+            let prevChapter: Int? = content.prev
             audioPlayer.load(
                 slug: slug,
                 chapter: chapter,
@@ -56,7 +57,8 @@ final class ChapterReaderViewModel: ObservableObject {
                 voice: settings.voice,
                 speed: settings.speed,
                 chapters: content.chapters,
-                nextChapter: nextChapter
+                nextChapter: nextChapter,
+                prevChapter: prevChapter
             )
         }
     }

ios/LibNovel/LibNovel/Views/BookDetail/BookDetailView.swift

@@ -86,7 +86,7 @@ struct BookDetailView: View {
                 Button(summaryExpanded ? "Less" : "More") {
                     withAnimation { summaryExpanded.toggle() }
                 }
-                .font(.caption.bold())
+                .font(.caption.bold()) 
                 .foregroundStyle(.amber)
             }
         }

ios/LibNovel/LibNovel/Views/ChapterReader/ChapterReaderView.swift

@@ -61,6 +61,14 @@ struct ChapterReaderView: View {
                 vm.navigateTo = next
             }
         }
+        .onReceive(NotificationCenter.default.publisher(for: .skipToNextChapter)) { note in
+            guard let next = note.userInfo?["next"] as? Int else { return }
+            vm.navigateTo = next
+        }
+        .onReceive(NotificationCenter.default.publisher(for: .skipToPrevChapter)) { note in
+            guard let prev = note.userInfo?["prev"] as? Int else { return }
+            vm.navigateTo = prev
+        }
         .navigationDestination(isPresented: Binding(
             get: { vm.navigateTo != nil },
             set: { if !$0 { vm.navigateTo = nil } }