fix(store): replace ZStack overlay sticky approach with native pinnedViews + reliable scroll tracking

- Use LazyVStack(pinnedViews: [.sectionHeaders]) for native section header stickiness
- Move ScrollOffsetReader outside LazyVStack (sibling) to prevent lazy-unload breaking scroll tracking
- Add baseline capture to ScrollOffsetReader to correctly normalize offset regardless of ScrollView content insets
- Apply safeAreaTop padding to categoryTabs only when pinned (isCategoryTabsPinned), preventing oversized header before scroll
- Remove complex ZStack dual-tabs overlay, stickyProgress logic, and categoryTabsStickyProgress
- categoryTabs now accepts isPinned flag with easeInOut(0.15s) animation on pin transition

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

pedi-foods/Sources/PediFoods/Views/Main/StoreDetailView.swift

@@ -34,15 +34,10 @@ struct StoreDetailView: View {
     @State var didLoad = false
     @State var categoryHeaderOffsets: [String: CGFloat] = [:]
     @State var isProgrammaticCategoryScroll = false
-    @State var scrollOffset: CGFloat = 0
-    var safeAreaTop: CGFloat {
-        #if canImport(UIKit)
-        return UIDevice.appSafeAreaTop
-        #else
-        return 0.0
-        #endif
-    }
     @State var isFavoriteRequestInFlight = false
+    @State var scrollOffset: CGFloat = 0
+
+    var isCategoryTabsPinned: Bool { scrollOffset >= topSectionHeight }
 
     let cardTopInset: CGFloat = 180
     let summaryCardBaseHeight: CGFloat = 212
@@ -52,48 +47,23 @@ struct StoreDetailView: View {
 
     var body: some View {
         ScrollViewReader { proxy in
-            let stickyProgress = categoryTabsStickyProgress(safeTop: safeAreaTop)
-
-            ZStack(alignment: .top) {
-                AppColors.backgroundLight.ignoresSafeArea()
-
-                ScrollView(showsIndicators: false) {
-                    LazyVStack(spacing: 0) {
-                        topSection
-                        Section {
-                            sectionedProducts
-                        } header: {
-                            categoryTabs(proxy: proxy, topExtension: 0, stickyProgress: 1)
-                                .opacity(Double(1 - stickyProgress))
-                        }
-                    }
-                    .background(
-                        GeometryReader { geometry in
-                            Color.clear.preference(
-                                key: ScrollOffsetPreferenceKey.self,
-                                value: geometry.frame(in: .named(StoreDetailScrollCoordinateSpace.name)).minY
-                            )
-                        }
-                    )
-                }
-                .coordinateSpace(name: StoreDetailScrollCoordinateSpace.name)
-                .onPreferenceChange(ScrollOffsetPreferenceKey.self) { minY in
-                    let normalizedOffset = max(0, -minY)
-                    if abs(scrollOffset - normalizedOffset) > 0.5 {
-                        scrollOffset = normalizedOffset
+            ScrollView(showsIndicators: false) {
+                ScrollOffsetReader(offsetY: $scrollOffset)
+                LazyVStack(spacing: 0, pinnedViews: [.sectionHeaders]) {
+                    topSection
+                    Section {
+                        sectionedProducts
+                    } header: {
+                        categoryTabs(proxy: proxy, isPinned: isCategoryTabsPinned)
                     }
                 }
-                .refreshable {
-                    await loadStoreData(forceRefresh: true)
-                }
-                .ignoresSafeArea(edges: .top)
-
-                categoryTabs(proxy: proxy, topExtension: stickyProgress * safeAreaTop, stickyProgress: 1)
-                    .opacity(Double(stickyProgress))
-                    .allowsHitTesting(stickyProgress > 0.1)
-                    .offset(y: safeAreaTop)
+            }
+            .coordinateSpace(name: StoreDetailScrollCoordinateSpace.name)
+            .refreshable {
+                await loadStoreData(forceRefresh: true)
             }
             .ignoresSafeArea(edges: .top)
+            .background(AppColors.backgroundLight)
             .saturation(isStoreOpen ? 1 : 0)
         }
         .navigationBarBackButtonHidden(true)