iOS: wire prev/next chapter buttons and add prefetch indicator

- Full player prev/next buttons now dismiss the player before navigating (allows user to see chapter change)
- Added amber loading indicator on next chapter button when prefetching audio (both mini and full player)
- Indicator appears as small ProgressView in bottom-right corner of forward button

ios/LibNovel/LibNovel/Views/Player/PlayerViews.swift

@@ -78,9 +78,26 @@ struct MiniPlayerView: View {
                             )
                         }
                     } label: {
+                        ZStack {
                             Image(systemName: "forward.end.fill")
                                 .font(.system(size: 24, weight: .semibold))
                                 .foregroundStyle(.white)
+                            
+                            // Show small loading indicator if next chapter is being prefetched
+                            if audioPlayer.nextPrefetchStatus == .prefetching {
+                                VStack {
+                                    Spacer()
+                                    HStack {
+                                        Spacer()
+                                        ProgressView()
+                                            .scaleEffect(0.5)
+                                            .tint(.amber)
+                                            .padding(2)
+                                            .background(Circle().fill(.black.opacity(0.6)))
+                                    }
+                                }
+                            }
+                        }
                         .frame(width: 44, height: 44)
                         .contentShape(Rectangle())
                     }
@@ -395,6 +412,7 @@ struct FullPlayerView: View {
                     // ← previous chapter
                     Button {
                         if let prev = audioPlayer.prevChapter {
+                            onDismiss()
                             NotificationCenter.default.post(
                                 name: .skipToPrevChapter,
                                 object: nil,
@@ -433,6 +451,7 @@ struct FullPlayerView: View {
                     // → next chapter
                     Button {
                         if let next = audioPlayer.nextChapter {
+                            onDismiss()
                             NotificationCenter.default.post(
                                 name: .skipToNextChapter,
                                 object: nil,
@@ -440,9 +459,26 @@ struct FullPlayerView: View {
                             )
                         }
                     } label: {
+                        ZStack {
                             Image(systemName: "forward.end.fill")
                                 .font(.system(size: 32, weight: .regular))
                                 .foregroundStyle(.white.opacity(0.9))
+                            
+                            // Show small loading indicator if next chapter is being prefetched
+                            if audioPlayer.nextPrefetchStatus == .prefetching {
+                                VStack {
+                                    Spacer()
+                                    HStack {
+                                        Spacer()
+                                        ProgressView()
+                                            .scaleEffect(0.6)
+                                            .tint(.amber)
+                                            .padding(4)
+                                            .background(Circle().fill(.black.opacity(0.6)))
+                                    }
+                                }
+                            }
+                        }
                         .frame(maxWidth: .infinity)
                     }
                     .buttonStyle(.plain)