feat: scroll-based mark-as-read with geometry tracking + navigation protection

Uses GeometryReader + coordinate space to track entry positions —
NOT onAppear/onDisappear.

How it works:
1. ScrollView has a named coordinate space ("readerScroll")
2. Invisible anchor at top measures scroll offset via PreferenceKey
3. Each entry row has a background GeometryReader that tracks its
   frame in the scroll coordinate space
4. onChange(of: maxY) detects when an entry's bottom edge crosses
   above the viewport top (oldMaxY >= 0 → newMaxY < 0)
5. Entry is marked read only when ALL conditions are true:
   - trackingActive (user scrolled down >100pt)
   - isScrollingDown (current direction is down)
   - entry is unread
   - entry hasn't been marked by scroll already
   - entry's bottom edge just crossed above viewport

Navigation protection:
- onAppear resets trackingActive = false and cumulativeDown = 0
- When returning from an article, tracking is suspended
- User must scroll down 100pt before tracking reactivates
- This prevents all visible entries from being marked read on
  navigation back (they were already below viewport, not crossing)
- Scrolling up never marks anything (isScrollingDown = false)

State updates are local-first (immediate) with background API sync.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ios/Platform/Platform/Features/Reader/Views/EntryListView.swift

@@ -1,9 +1,31 @@
 import SwiftUI
 
+// MARK: - Scroll Offset Preference Key
+
+private struct ScrollOffsetKey: PreferenceKey {
+    static var defaultValue: CGFloat = 0
+    static func reduce(value: inout CGFloat, nextValue: () -> CGFloat) {
+        value = nextValue()
+    }
+}
+
+// MARK: - Entry List View
+
 struct EntryListView: View {
     @Bindable var vm: ReaderViewModel
     var isCardView: Bool = true
 
+    // Scroll-based read tracking
+    @State private var previousOffset: CGFloat = 0
+    @State private var isScrollingDown = false
+    @State private var trackingActive = false
+    @State private var cumulativeDown: CGFloat = 0
+    @State private var markedByScroll: Set<Int> = []
+
+    // Require 100pt of genuine downward scroll before tracking activates.
+    // Prevents mass-marking when returning from article navigation.
+    private let activationThreshold: CGFloat = 100
+
     var body: some View {
         if vm.isLoading && vm.entries.isEmpty {
             LoadingView()
@@ -19,12 +41,32 @@ struct EntryListView: View {
             .frame(maxWidth: .infinity, maxHeight: .infinity)
         } else {
             ScrollView {
+                // Invisible anchor to measure scroll offset
+                GeometryReader { geo in
+                    Color.clear.preference(
+                        key: ScrollOffsetKey.self,
+                        value: geo.frame(in: .named("readerScroll")).minY
+                    )
+                }
+                .frame(height: 0)
+
                 if isCardView {
                     cardLayout
                 } else {
                     listLayout
                 }
             }
+            .coordinateSpace(name: "readerScroll")
+            .onPreferenceChange(ScrollOffsetKey.self) { value in
+                handleScrollOffset(-value)
+            }
+            .onAppear {
+                // Reset tracking on every appear (including back from article).
+                // User must scroll down 100pt before marking resumes.
+                trackingActive = false
+                cumulativeDown = 0
+                isScrollingDown = false
+            }
             .refreshable {
                 await vm.refresh()
             }
@@ -34,12 +76,74 @@ struct EntryListView: View {
         }
     }
 
+    // MARK: - Scroll Direction + Activation
+
+    private func handleScrollOffset(_ newOffset: CGFloat) {
+        let delta = newOffset - previousOffset
+        previousOffset = newOffset
+
+        // Ignore tiny deltas (noise from layout)
+        guard abs(delta) > 1 else { return }
+
+        if delta > 0 {
+            // Scrolling down
+            isScrollingDown = true
+            cumulativeDown += delta
+            if cumulativeDown > activationThreshold {
+                trackingActive = true
+            }
+        } else {
+            // Scrolling up — pause tracking, don't reset cumulative
+            isScrollingDown = false
+        }
+    }
+
+    // MARK: - Entry Row with Scroll-Read Tracking
+
+    private func scrollTracked(_ entry: ReaderEntry, content: some View) -> some View {
+        content
+            .background(
+                GeometryReader { geo in
+                    Color.clear
+                        .onChange(of: geo.frame(in: .named("readerScroll")).maxY) { oldMaxY, newMaxY in
+                            // Only mark if:
+                            // 1. Tracking is active (user scrolled down 100pt)
+                            // 2. User is scrolling downward
+                            // 3. Entry is unread
+                            // 4. Entry hasn't been marked by scroll already
+                            // 5. Entry's bottom edge just crossed above viewport (old >= 0, new < 0)
+                            guard trackingActive,
+                                  isScrollingDown,
+                                  !entry.isRead,
+                                  !markedByScroll.contains(entry.id),
+                                  oldMaxY >= 0,
+                                  newMaxY < 0 else { return }
+
+                            markedByScroll.insert(entry.id)
+
+                            // Local-first: update immediately
+                            if let idx = vm.entries.firstIndex(where: { $0.id == entry.id }) {
+                                vm.entries[idx].status = "read"
+                            }
+
+                            // API sync in background
+                            Task {
+                                let api = ReaderAPI()
+                                try? await api.markEntries(ids: [entry.id], status: "read")
+                                vm.counters = try? await api.getCounters()
+                            }
+                        }
+                }
+            )
+    }
+
     // MARK: - Card Layout
 
     private var cardLayout: some View {
         LazyVStack(spacing: 12) {
             ForEach(vm.entries) { entry in
-                NavigationLink(value: entry) {
+                scrollTracked(entry,
+                    content: NavigationLink(value: entry) {
                         EntryCardView(entry: entry)
                     }
                     .buttonStyle(.plain)
@@ -47,6 +151,7 @@ struct EntryListView: View {
                     .contextMenu {
                         entryContextMenu(entry: entry, vm: vm)
                     }
+                )
             }
 
             loadMoreTrigger
@@ -62,7 +167,8 @@ struct EntryListView: View {
     private var listLayout: some View {
         LazyVStack(spacing: 0) {
             ForEach(vm.entries) { entry in
-                NavigationLink(value: entry) {
+                scrollTracked(entry,
+                    content: NavigationLink(value: entry) {
                         EntryRowView(entry: entry)
                     }
                     .buttonStyle(.plain)
@@ -70,6 +176,7 @@ struct EntryListView: View {
                     .contextMenu {
                         entryContextMenu(entry: entry, vm: vm)
                     }
+                )
 
                 Divider()
                     .padding(.leading, 36)
@@ -114,7 +221,6 @@ struct EntryCardView: View {
                             .frame(height: 180)
                             .clipped()
                     default:
-                        // Reserve space during load to prevent layout jump
                         Rectangle()
                             .fill(Color.surfaceCard)
                             .frame(height: 180)