iOS: fix audio polling, AVPlayer stability, and misc UX issues

- AudioPlayerService: replace loading/generating states with a single
  .generating state; presign fast path before triggering TTS; fix URL
  resolution for relative paths; cache cover artwork to avoid re-downloads;
  fix duration KVO race (durationObserver); use toleranceBefore/After:zero
  for accurate seeking; prefetch next chapter unconditionally (not just when
  autoNext is on); handle auto-next internally on playback finish
- APIClient: fix URL construction (appendingPathComponent encodes slashes);
  add verbose debug logging for all requests/responses/decoding errors;
  fix sessions() to unwrap {sessions:[]} envelope; fix BrowseResponse
  CodingKey hasNext → camelCase
- AudioGenerateResponse: update to synchronous {url, filename} shape
- Models: remove redundant AudioStatus enum; remove CodingKeys from
  UserSettings (server now sends camelCase)
- Views: fix alert bindings (.constant → proper two-way Binding); add
  error+retry UI to BrowseView; add pull-to-refresh to browse list;
  fix ChapterReaderView to show error state and use dynamic WKWebView
  height; fix HomeView HStack alignment; only treat audio as current
  if the player isActive; suppress CancellationError from error UI

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

@@ -18,19 +18,46 @@ struct ChapterReaderView: View {
     }
 
     var body: some View {
+        let _ = print("[ChapterReaderView] body eval — slug=\(slug) ch=\(chapterNumber) isLoading=\(vm.isLoading) hasContent=\(vm.content != nil) error=\(vm.error ?? "nil")")
         Group {
             if vm.isLoading {
+                let _ = print("[ChapterReaderView] branch: LOADING")
                 ProgressView().frame(maxWidth: .infinity, maxHeight: .infinity)
             } else if let content = vm.content {
+                let _ = print("[ChapterReaderView] branch: CONTENT html=\(content.html.count)chars title='\(content.chapter.title)'")
                 readerContent(content)
+            } else if let errMsg = vm.error {
+                let _ = print("[ChapterReaderView] branch: ERROR '\(errMsg)'")
+                VStack(spacing: 16) {
+                    Image(systemName: "exclamationmark.triangle")
+                        .font(.largeTitle)
+                        .foregroundStyle(.orange)
+                    Text(errMsg)
+                        .multilineTextAlignment(.center)
+                        .foregroundStyle(.secondary)
+                        .padding(.horizontal)
+                    Button("Retry") { Task { await vm.load() } }
+                        .buttonStyle(.borderedProminent)
+                        .tint(.amber)
+                }
+                .frame(maxWidth: .infinity, maxHeight: .infinity)
+            } else {
+                let _ = print("[ChapterReaderView] branch: BLANK (no loading, no content, no error)")
+                Color.clear
             }
         }
         .navigationTitle(vm.content.map { "Ch.\($0.chapter.number)" } ?? "")
         .navigationBarTitleDisplayMode(.inline)
         .toolbar { audioToolbarButton }
-        .task { await vm.load() }
+        .task {
+            print("[ChapterReaderView] .task fired — calling vm.load()")
+            await vm.load()
+            print("[ChapterReaderView] .task completed")
+        }
         .onReceive(NotificationCenter.default.publisher(for: .audioDidFinishChapter)) { note in
-            if let next = note.userInfo?["next"] as? Int {
+            guard let next = note.userInfo?["next"] as? Int else { return }
+            let shouldAutoNavigate = note.userInfo?["autoNext"] as? Bool ?? false
+            if shouldAutoNavigate {
                 vm.navigateTo = next
             }
         }
@@ -42,15 +69,15 @@ struct ChapterReaderView: View {
                 ChapterReaderView(slug: slug, chapterNumber: next)
             }
         }
-        .alert("Error", isPresented: .constant(vm.error != nil)) {
-            Button("OK") { vm.error = nil }
-        } message: { Text(vm.error ?? "") }
     }
 
     // MARK: - Content
 
+    @State private var webHeight: CGFloat = 800
+
     @ViewBuilder
     private func readerContent(_ content: ChapterResponse) -> some View {
+        let _ = print("[ChapterReaderView] readerContent — html=\(content.html.count)chars webHeight=\(webHeight)")
         ScrollView {
             VStack(alignment: .leading, spacing: 16) {
                 // Header
@@ -68,7 +95,8 @@ struct ChapterReaderView: View {
                 Divider()
 
                 // Chapter body
-                HTMLContentView(html: content.html)
+                HTMLContentView(html: content.html, height: $webHeight)
+                    .frame(height: webHeight)
                     .padding(.horizontal)
 
                 Divider()
@@ -119,30 +147,62 @@ struct ChapterReaderView: View {
 
 struct HTMLContentView: UIViewRepresentable {
     let html: String
+    @Binding var height: CGFloat
+
+    func makeCoordinator() -> Coordinator { Coordinator(self) }
 
     func makeUIView(context: Context) -> WKWebView {
         let wv = WKWebView()
         wv.scrollView.isScrollEnabled = false
         wv.isOpaque = false
         wv.backgroundColor = .clear
+        wv.scrollView.backgroundColor = .clear
+        wv.navigationDelegate = context.coordinator
         return wv
     }
 
     func updateUIView(_ uiView: WKWebView, context: Context) {
+        let isDark = UITraitCollection.current.userInterfaceStyle == .dark
+        let textColor = isDark ? "#e5e5e5" : "#1a1a1a"
         let css = """
         body {
             font-family: -apple-system, Georgia, serif;
             font-size: 17px;
             line-height: 1.7;
-            color: \(UITraitCollection.current.userInterfaceStyle == .dark ? "#e5e5e5" : "#1a1a1a");
+            color: \(textColor);
             background: transparent;
             margin: 0; padding: 0;
+            word-break: break-word;
         }
         p { margin: 0 0 1em 0; }
         """
         let wrapped = "<html><head><style>\(css)</style><meta name='viewport' content='width=device-width, initial-scale=1'></head><body>\(html)</body></html>"
+        print("[HTMLContentView] updateUIView — html=\(html.count)chars loading into WKWebView")
         uiView.loadHTMLString(wrapped, baseURL: nil)
     }
+
+    class Coordinator: NSObject, WKNavigationDelegate {
+        var parent: HTMLContentView
+        init(_ parent: HTMLContentView) { self.parent = parent }
+
+        func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
+            print("[HTMLContentView] didFinish — evaluating scrollHeight")
+            webView.evaluateJavaScript("document.body.scrollHeight") { result, error in
+                DispatchQueue.main.async {
+                    print("[HTMLContentView] scrollHeight result=\(String(describing: result)) error=\(String(describing: error))")
+                    if let h = result as? CGFloat, h > 0 {
+                        print("[HTMLContentView] height set to CGFloat \(h)")
+                        self.parent.height = h
+                    } else if let h = result as? Double, h > 0 {
+                        print("[HTMLContentView] height set to Double \(h)")
+                        self.parent.height = CGFloat(h)
+                    } else {
+                        print("[HTMLContentView] ⚠️ could not read height — keeping \(self.parent.height)")
+                    }
+                }
+            }
+        }
+    }
 }
 
 // MARK: - Reverse label style (icon on right)