fix: scroll mark-as-read crossing event missed by LazyVStack recycling

ROOT CAUSE: The exact crossing condition (oldMaxY >= 0 && newMaxY < 0)
required onChange to fire at the exact moment maxY crosses zero. But
LazyVStack recycles views when they scroll off-screen, destroying the
GeometryReader before the crossing event is delivered. The entry goes
from maxY=15 to being recycled — onChange never sees maxY go negative.

FIX: Replace exact crossing with position check (newMaxY < 0). The
entry just needs to be fully above the viewport. The other 5 guards
prevent false positives:
  1. trackingActive (scrolled past threshold)
  2. isScrollingDown
  3. !entry.isRead
  4. !markedByScroll (dedup)
  5. wasVisible (was >=50% visible)

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

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

@@ -131,21 +131,24 @@ struct EntryListView: View {
                                 wasVisible.insert(entry.id)
                             }
                         }
-                        .onChange(of: frame.maxY) { oldMaxY, newMaxY in
+                        .onChange(of: frame.maxY) { _, newMaxY in
-                            // Mark as read when entry scrolls above viewport.
+                            // Mark as read when entry is above viewport.
-                            // All 6 conditions must be true:
+                            // 5 conditions must be true:
                             // 1. Tracking active (scrolled past dynamic threshold)
                             // 2. Scrolling downward
                             // 3. Entry is unread
                             // 4. Not already marked by scroll
                             // 5. Was >=50% visible at some point (genuinely seen)
-                            // 6. Bottom edge just crossed above viewport
+                            //
+                            // We check newMaxY < 0 (entry fully above viewport)
+                            // instead of requiring an exact crossing event, because
+                            // LazyVStack can recycle the view between onChange calls,
+                            // causing the 0-boundary crossing to never be delivered.
                             guard trackingActive,
                                   isScrollingDown,
                                   !entry.isRead,
                                   !markedByScroll.contains(entry.id),
                                   wasVisible.contains(entry.id),
-                                  oldMaxY >= 0,
                                   newMaxY < 0 else { return }
 
                             markedByScroll.insert(entry.id)