Add reading progress tracking

- BrowserState: inject scroll-tracking JS after page load, report position
  via WKScriptMessageHandler (weak ref to avoid retain cycle)
- BrowserView: thin blue progress bar at top of viewport; saves progress
  to UserDefaults on dismiss; restores scroll position on revisit
- BookmarkRow: 2px progress bar below tags for partially-read articles
- BookmarksView: loads ReadingProgress.all() on appear, refreshes when
  browser sheet dismisses
- ReadingProgress: static helper for UserDefaults-backed [url: Double] store;
  removes entry when article is fully read (≥99%)

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

Marks/Views/BrowserView.swift

@@ -1,6 +1,32 @@
 import SwiftUI
 import WebKit
 
+// MARK: - Reading progress persistence
+
+enum ReadingProgress {
+    private static let key = "readingProgress"
+
+    static func get(url: String) -> Double {
+        (UserDefaults.standard.dictionary(forKey: key) as? [String: Double])?[url] ?? 0
+    }
+
+    static func set(url: String, progress: Double) {
+        var store = (UserDefaults.standard.dictionary(forKey: key) as? [String: Double]) ?? [:]
+        if progress >= 0.99 {
+            store.removeValue(forKey: url) // fully read — clean up
+        } else {
+            store[url] = progress
+        }
+        UserDefaults.standard.set(store, forKey: key)
+    }
+
+    static func all() -> [String: Double] {
+        (UserDefaults.standard.dictionary(forKey: key) as? [String: Double]) ?? [:]
+    }
+}
+
+// MARK: - BrowserState
+
 @Observable
 final class BrowserState: NSObject, WKNavigationDelegate {
     let webView: WKWebView
@@ -9,16 +35,34 @@ final class BrowserState: NSObject, WKNavigationDelegate {
     var canGoForward = false
     var pageTitle = ""
     var currentURL: URL?
+    var readingProgress: Double = 0
+
+    // Weak wrapper breaks WKUserContentController's strong retain of the handler
+    private final class ScrollHandler: NSObject, WKScriptMessageHandler {
+        weak var state: BrowserState?
+        init(_ state: BrowserState) { self.state = state }
+        func userContentController(_ c: WKUserContentController, didReceive msg: WKScriptMessage) {
+            if let p = msg.body as? Double { state?.readingProgress = p }
+        }
+    }
+    private var scrollHandler: ScrollHandler?
 
     init(url: URL) {
         let config = WKWebViewConfiguration()
         config.allowsInlineMediaPlayback = true
         webView = WKWebView(frame: .zero, configuration: config)
         super.init()
+        let handler = ScrollHandler(self)
+        scrollHandler = handler
+        webView.configuration.userContentController.add(handler, name: "scrollProgress")
         webView.navigationDelegate = self
         webView.load(URLRequest(url: url))
     }
 
+    deinit {
+        webView.configuration.userContentController.removeScriptMessageHandler(forName: "scrollProgress")
+    }
+
     func webView(_ webView: WKWebView, didStartProvisionalNavigation _: WKNavigation!) {
         isLoading = true
     }
@@ -35,24 +79,46 @@ final class BrowserState: NSObject, WKNavigationDelegate {
         canGoForward = webView.canGoForward
         pageTitle = webView.title ?? ""
         currentURL = webView.url
+
+        // Restore persisted progress, then start tracking scroll
+        if let urlStr = webView.url?.absoluteString {
+            let saved = ReadingProgress.get(url: urlStr)
+            if saved > 0 {
+                let pct = saved * 100
+                webView.evaluateJavaScript("window.scrollTo(0, (document.body.scrollHeight - window.innerHeight) * \(pct) / 100)", completionHandler: nil)
+            }
+        }
+        webView.evaluateJavaScript(scrollTrackingJS, completionHandler: nil)
     }
 
-    func webView(_: WKWebView, didFail _: WKNavigation!, withError _: Error) {
-        isLoading = false
-    }
-
-    func webView(_: WKWebView, didFailProvisionalNavigation _: WKNavigation!, withError _: Error) {
-        isLoading = false
-    }
+    func webView(_: WKWebView, didFail _: WKNavigation!, withError _: Error) { isLoading = false }
+    func webView(_: WKWebView, didFailProvisionalNavigation _: WKNavigation!, withError _: Error) { isLoading = false }
 
     func enterReaderMode(completion: @escaping () -> Void) {
         webView.evaluateJavaScript(readerModeJS) { _, _ in
-            DispatchQueue.main.async { completion() }
+            DispatchQueue.main.async {
+                completion()
+                self.webView.evaluateJavaScript(self.scrollTrackingJS, completionHandler: nil)
+            }
         }
     }
 
-    func exitReaderMode() {
-        webView.reload()
+    func exitReaderMode() { webView.reload() }
+
+    private var scrollTrackingJS: String {
+        """
+        (function(){
+            function report(){
+                var h=document.body.scrollHeight-window.innerHeight;
+                var p=h>0?window.scrollY/h:0;
+                window.webkit.messageHandlers.scrollProgress.postMessage(Math.min(1,Math.max(0,p)));
+            }
+            window.removeEventListener('scroll',window._marksScrollFn);
+            window._marksScrollFn=report;
+            window.addEventListener('scroll',report,{passive:true});
+            report();
+        })();
+        """
     }
 
     private var readerModeJS: String {
@@ -106,12 +172,16 @@ final class BrowserState: NSObject, WKNavigationDelegate {
     }
 }
 
+// MARK: - WebView representable
+
 private struct WebViewRepresentable: UIViewRepresentable {
     let webView: WKWebView
     func makeUIView(context: Context) -> WKWebView { webView }
     func updateUIView(_ uiView: WKWebView, context: Context) {}
 }
 
+// MARK: - BrowserView
+
 struct BrowserView: View {
     let initialURL: URL
     let initialTitle: String
@@ -136,6 +206,17 @@ struct BrowserView: View {
                 WebViewRepresentable(webView: state.webView)
                     .ignoresSafeArea(edges: .bottom)
 
+                // Reading progress bar
+                if state.readingProgress > 0.01 && state.readingProgress < 0.99 {
+                    GeometryReader { geo in
+                        Rectangle()
+                            .fill(Color.blue.opacity(0.7))
+                            .frame(width: geo.size.width * state.readingProgress, height: 3)
+                    }
+                    .frame(height: 3)
+                    .animation(.linear(duration: 0.1), value: state.readingProgress)
+                }
+
                 if state.isLoading {
                     ProgressView()
                         .padding(.top, 8)
@@ -151,25 +232,19 @@ struct BrowserView: View {
                     }
                 }
                 ToolbarItem(placement: .topBarTrailing) {
-                    Button {
-                        openURL(state.currentURL ?? initialURL)
-                    } label: {
+                    Button { openURL(state.currentURL ?? initialURL) } label: {
                         Image(systemName: "safari")
                     }
                 }
                 ToolbarItemGroup(placement: .bottomBar) {
-                    Button {
-                        state.webView.goBack()
-                    } label: {
+                    Button { state.webView.goBack() } label: {
                         Image(systemName: "chevron.left")
                     }
                     .disabled(!state.canGoBack)
 
                     Spacer()
 
-                    Button {
-                        state.webView.goForward()
-                    } label: {
+                    Button { state.webView.goForward() } label: {
                         Image(systemName: "chevron.right")
                     }
                     .disabled(!state.canGoForward)
@@ -177,12 +252,8 @@ struct BrowserView: View {
                     Spacer()
 
                     Button {
-                        if readerMode {
-                            state.exitReaderMode()
-                            readerMode = false
-                        } else {
-                            state.enterReaderMode { readerMode = true }
-                        }
+                        if readerMode { state.exitReaderMode(); readerMode = false }
+                        else { state.enterReaderMode { readerMode = true } }
                     } label: {
                         Image(systemName: readerMode ? "doc.text.fill" : "doc.text")
                     }
@@ -191,13 +262,10 @@ struct BrowserView: View {
                     Spacer()
 
                     if claude != nil {
-                        Button {
-                            showPodcast = true
-                        } label: {
+                        Button { showPodcast = true } label: {
                             Image(systemName: "headphones")
                         }
                         .disabled(state.isLoading)
-
                         Spacer()
                     }
 
@@ -207,10 +275,14 @@ struct BrowserView: View {
                 }
             }
         }
+        .onDisappear {
+            let urlStr = (state.currentURL ?? initialURL).absoluteString
+            let p = state.readingProgress
+            if p > 0.01 { ReadingProgress.set(url: urlStr, progress: p) }
+        }
         .sheet(isPresented: $showPodcast) {
             if let claude {
-                let url = (state.currentURL ?? initialURL).absoluteString
-                PodcastPlayerView(articleUrl: url, claude: claude)
+                PodcastPlayerView(articleUrl: (state.currentURL ?? initialURL).absoluteString, claude: claude)
             }
         }
     }